Experimental Work on Tube Design for Electron Affinity Measurement

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BXFEHIMEMfAL WORK 01

TUBE DESIGN FOR BDECTBGF &FFIHITY MMSUREIOTf

hj r\j& A lv in B* W&lz

A t h e s i s su b m itte d in p a r t i a l f u l f i l l m e n t o f tb s re q u ire m e n ts f o r th e degree o f D octor o f P h ilo so p h y in th e D epartm ent o f C hem istry in th e G raduate C ollege of th e S ta te U n iv e rs ity o f Iowa June 1950

ProQuest Number: 10666184

All rights reserved INFORMATION TO ALL USERS The quality o f this reproduction is d ep en d en t upon th e quality o f th e co p y submitted. In the unlikely ev en t that th e author did not send a co m p lete manuscript and there are missing p a g es, th ese will b e noted. Also, if material had to b e rem oved, a note will indicate the deletion.

uest. ProQuest 10666184 Published by ProQuest LLC (2017). Copyright o f the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346

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The a u th o r w ish e s t o e x p r e s s h i s t o P r o f e s s o r Georg© G lo e k le i th e s u g g e s tio n o f th e p ro b lem w ith w h ich t h i s [9 f o r h i s i n t e r e s t and d u r in g th e c o u r s e o f th e w o rk ,

g r a t e f u l l y acknow -

i s a ls o ex p ressed to th e G ra d u a te o f Iow a f o r t h e f o r th e p a s t ye*

• # • ' * • * " * * * « - *■*■**•

X

C h a p te r X

ICTROOTCTIOH I n a s tu d y o f t h e e l e c t r o n a f f i n i t y o f c a rb o n by G lo c k l e r and S a u s v i l l e (2 8 ) I t was fo u n d t h a t th e p r e s e n c e o f p o s i t i v e c a rb o n io n s was r e s p o n s i b l e f o r a te m p e r a tu r e t r e n d i n th e I o n - c u r r e n t r a t i o o b s e rv e d *

The p o s i t i v e c a r *

bon I o n s r e s u l t e d fro ® a h ig h p o t e n t i a l d ro p a c r o s s th e f ila m e n t *

The p u rp o s e o f t h i s i n v e s t i g a t i o n was t o d e t e r *

m ine I f a f i l a m e n t c o u ld fee p ro d u c e d w h ich

e lim in a te d th e

h ig h p o t e n t i a l d ro p an d h e n c e th e p o s i t i v e c a rb o n io n s w h ile o p e r a t i n g i n th e te m p e r a tu r e ra n g e o f 1 8 5 0 ° K t o 2 2 5 0 ° 1C*

I t c a n be s a i d t h a t a f i l a m e n t was c o n s t r u c t e d

w h ich p e r m i t t e d th e a t t a i n m e n t o f t h e s e te m p e r a tu r e s *

How­

e v e r , f u r t h e r d e v e lo p m e n t a lo n g th e l i n e s o f c o o l in g th e f i l a m e n t l e a d s w i l l be n e c e s s a r y b e f o r e th e tu b e w i l l b e c o m p le te ly s a t i s f a c t o r y f o r o p e r a tio n * H ot d i r e c t l y Im p lie d by th e m ain p ro b le m b u t o f d i r e c t i n t e r e s t w as a c o m p le te r e v ie w o f th e l i t e r a t u r e d e a l i n g w ith th e v a p o r p r e s s u r e o f c a rb o n a s a f u n c t i o n o f t e m p e r a tu r e .

The h e a t o f s u b lim a tio n o f c a rb o n h a s b e e n

d e te r m in e d many tim e s , b o th e x p e r i m e n t a l l y and by t h e o r e t i ­ c a l c a l c u l a t i o n s , b u t t h e r e s u l t s v a r y w id e l y .

2

C h a p te r I I THEGSETIGAL CQHSIDERATI0H3 COKCEHSIMG ELECTRON AFFINITY The e l e c t r o n a f f i n i t y o f a n e le m e n t I i s d e f in e d a s th e d e c r e a s e I n th e e n e rg y t h a t acco m p an ies th e f o llo w in g r e a c t i o n a t a b s o lu te z e ro s X + e~

*X *\

Many m ethods have b e e n u se d t o d e te rm in e th e e l e c ­ t r o n a f f i n i t y o f v a r io u s e le m e n ts*

G lo c k le r and L ind (4 )

d is c u s s t e n m ethods by w hich e l e c t r o n a f f i n i t y c a n b© d e t e r ­ m ined*

The f i r s t was t h a t o f B orn (16) who u s e d w hat i s now

c a l l e d a B o m C ycle w h ich in v o lv e s s e t t i n g up an e n e rg y c y c le w h e re in a l l th e e n e rg y c h a n g e s c o n c e rn e d a r e known e x ­ c e p t th e one w h ich i s t o b e d e te rm in e d *

As a n exam ple 0 con­

s i d e r th e f o llo w in g *

men ✓tu>

-

p (ffag i)

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ft(H aC l) H a(s)

♦ i C l 2 {g)

H a(s) I(H a)

s(N & )

* A b(C l2 5

*

H a(s5

♦ G l ‘" ( g ) -E (C 1 ) * c l (e)

w here B(H aCl) I s th e l a t t i c e e n e rg y o f th e EaCl c r y s t a l ; X(Ha)

I s th e I o n i s a t i o n e n e rg y o f sodium ?

E{C1)

i s th e e l e c t r o n a f f i n i t y o f c h l o r i n e atom s?

3 3 (Ha)

1M

th e h e a t o f s u b lim a tio n o f so d iu m ;

B tG ig )

is

t h e b o a t o f d i s s o c i a t i o n o f C ls l

Q (H aCl)

Is

th e b e a t o f f o r m a tio n o f H a d

The f i r s t law o f therm odynam ics r e q u i r e s t h a t th e m m o f a l l e n e r g i e s w hereby n&Cl i s b ro u g h t b ack t o

its

o r i g i n a l s t a t e a f t e r u n d e rg o in g th e ch a n g e s o f th e c y c le i s z e ro *

T h e r e f o re

(Sa61)+1(Ha}-B{01)*S(Ba)

(Slg )

{Bad, J■*©

(1)

and B {01)« -0{H aC l)+I(H a}+S(H a)X * 1 “

th e i o n i z a t i o n p o t e n t i a l o f Y*% w hich i s th e n e g a tiv e o f th e e l e c t r o n a f f i n i t y o f Y & can be r e a d i l y d e te rm in e d *

M assey( 8),

who h a s re v ie w th e f i e l d * c o n s id e r s t h i s t o be a d i r e c t and

4 r e l i a b l e means o f m e a su rin g th e e l e c t r o n a f f i n i t y * P u r e ly t h e o r e t i c a l c a l c u l a t i o n s o f e l e c t r o n a f f i n ­ i t i e s h a v e b ee n c a r r i e d o u t s t a r t i n g w ith B ohr th e o r y o f th e a tm

(1 5 ) * An Im provem ent on t h i s c a l c u l a t i o n was m & e b y

P a u lin g (SB) u s in g a s c r e e n in g c o n s t a n t and f u r t h e r im prove­ m ent fey G -lockler (2 3 ) fey f i n d i n g th e v a r i a t i o n o f th e s c r e e n ­ in g c o n s t a n t w ith ato m ic number*

U sin g quantum m e c h a n ic s ,

H y lle r& s (3 2 )( 5 3 ) an d B eth e (1 4 ) h av e o b ta in e d w hat i s co n ­ s i d e r e d a v e r y r e l i a b l e v a lu e i n th e c a s e o f h y d ro g en * Ta-Tou Wtt (6 3 ) r e p o r t s v a l u e s f o r h e liu m and l i t h i u m o b t a i n ­ e d i n l i t o m aim er, b u t c a l c u l a t i o n s f o r any l a r g e r atom s h av e n o t b ee n c a r r i e d o u t due to th e m a th e m a tic a l c o m p le x i­ t i e s i n h e r e n t i n quantum m e c h a n ic a l tr e a tm e n t . G lo c k le r (24) h a s d e r iv e d e m p ir i c a l v a lu e s o f e l e c t r o n a f f i n i t i e s by e x t r a p o l a t i o n o f th e M oseley c u rv e s f o r known i o n i s a t i o n p o t e n t i a l s o f th o s e "strip p e d * * atom s i s o e l e c t r o n i e w ith th e n e g a tiv e i o n . I * a Z2 ~ b% ♦ e

By assu m in g a r e l a t i o n (sj

w here 1 i s th e i o n i z a t i o n p o t e n t i a l o f th e atom o f ato m ic number Z a , b , and c a r e c o n s t a n t s c a l c u l a t e d from known v a lu e s o f I , he o b ta in e d v a lu e s f o r th e e l e c t r o n a f f i n i t y o f some tw e n ty atom s*

I n g e n e r a l th e r e s u l t s o b ta in e d by t h i s m ethod a r e

5 c o n s i s t e n t w i t h w h at a p p e a r s t o b e th e n a t u r e o f th e v a r i a ­ tio n

o f e l e c t r o n a f f i n i t y fro m e le m e n t t o e le m e n t*

H ellm an u an d Mamotenko (4 5 ) h av e s i n c e c a r r i e d o u t s i m i l a r e m p i r i c a l c a l c u l a t i o n s w i t h r e s u l t s s l i g h t l y d i f f e r e n t fro m t h o s e o f G lo c k le r ^ b u t t h e l a c k o f e x p e r im e n ta l m e asu rem e n ts f o r t h e m a j o r i t y o f th e atom s m akes a c r i t i c a l c o m p a riso n o f t h e two s e t s o f v a l u e s im p o s s ib le *

G lo c k le r (2 8 ) m ore

r e c e n t l y h a s u s e d a n e m p i r i c a l r e l a t i o n s h i p f o r th e e s tim a ­ t i o n o f th e e l e c t r o n a f f i n i t y o f th e c a rb o n atom b a s e d on t h e i o n i s a t i o n p o t e n t i a l s and a to m ic num ber o f th e i s o e l e c t r o n l e s e q u e n c e 0*% 1* 0 % P * % an d He'1'44'*

T h is r e l a t i o n ­

s h ip I s X* « bZ ♦ c w here I i s th e I o n i s a t i o n p o t e n t i a l Z i s th e a to m ic num ber a , b , and c a r e c o n s t a n t s w ith th e v a lu e s 0*S75# 5*07 an d 16*828 r e s p e c t i v e l y * T h is r e l a t i o n s h i p r e p r o d u c e s th© i o n i s a t i o n p o t e n t i a l s o f 0% F 44, an d He444 t o a h ig h d e g re e o f a c c u r a c y and th e e x ­ t r a p o l a t e d v a lu e f o r t h e i o n i s a t i o n p o t e n t i a l o f n e g a t i v e c a rb o n a to m ic i o n i s v e r y l i k e l y a p r e t t y good e s tim a te * t h i s m ethod 2.2 e„v « was o b ta in e d a s th e e l e c t r o n a f f i n i t y o f c a rb o n * H o lla an d P i c c a r d I ( 5 4 ) ( 5 5 ) e v a lu a t e d th e e q u i l ­ ib r iu m c o n s t a n t f o r e l e c t r o n a tta c h m e n t r e a c t i o n s fro m th e

By

c h a n g e i n conductivity of" fla m e a w h ic h s u c h a r e a c t i o n p r o ­ d u c e s , an d i n t h i s way w ere a b l e t o m e asu re e l e c t r o n a f f i n i ­ tie s *

H ow ever, i n th o s e c a s e s w here c o m p a riso n w ith o t h e r

e x p e r i m e n ta l d a t a i s p o s s i b l e , t h e i r v a l u e s a p p e a r t o b e to o h ig h * Two o t h e r m eth o d s i n v o lv i n g th e m e a su re o f t h e e q u i l i b r i u m c o n s t a n t f o r e l e c t r o n a tta c h m e n t r e a c t i o n s h a v e b e e n u s e d f o r th e d e t e r m i n a t i o n o f e l e c t r o n a f f i n i t y *

One

o f t h e s e i s t h e s p a c e c h a rg e m eth o d o f ( H e c k le r an d C a lv in {26} (2 7 ) an d t h e o t h e r i s th e m a g n e tro n m ethod o f M ayer said o t h e r s { 1 9 } (4 3 )(4 7 } (4 8 )(4 9 ){ 6 2 } { 6 7 } «

B o th m eth o d s a r e b a s e d

on t h e same f u n d a m e n ta l c o n c e p ts w h ich w i l l now b e p r e s e n te d * The e q u i l i b r i u m c o n s t a n t , K, f o r th e e l e c t r o n a tta c h m e n t r e a c t i o n X(g> ♦ e*"(g} ** X * (g ) o c c u r r i n g a t o r n e a r a s u r f a c e S a t te m p e r a tu r e T (S ) 1 s t ^

P(x~)

r^ m * ¥ ( t r r

H)

w h ere 3 t(j) r e p r e s e n t s t h e p r e s s u r e o f t h e j t h s p e c ie s * When e q u i l i b r i u m i s e s t a b l i s h e d b etw e en th e co m p o n en ts o f t h e r e ­ a c t io n and th e s u r f a c e , th e num ber Z ( j } o f e a c h ty p e o f p a r t i c l e s t r i k i n g u n i t s u r f a c e p e r u n i t tim e e q u a ls t h e num­ b e r o f e a c h l e a v i n g th e u n i t s u r f a c e p e r u n i t tim e* i s r e l a t e d t o P { j) b y

7 * » ' • T « 4 7 F . 7T -

T h e re fo re Z m 1 1 ™ — IT T " {SlT' k ^ 8 ^ ^ “ x y ,JV a®“ 5 "X*® 0

K *

S in c e m (x ") an d m (x) d i f f e r o n ly b y th e m ass o f a s i n g l e e l e c t r o n , t h e i r m asses c a n b e c o n s id e r e d e q u a l and E q u a tio n ( 6) r e d u c e s t o K -

(2 x - / Z x Za - ) (2 < ff ie - k - P g ) " i

(7 )

2{x~}/&£©""), th e r a t i o o f io n s to e l e c t r o n s l e a v ­ in g u n i t s u r f a c e p e r u n i t tim e i s a l s o e q u a l

t o th e r a t i o o f

th e e l e c t r i c a l c u r r e n t s i ( j } c a r r i e d by e a c h and i s a d i r e c t ­ l y m e a s u ra b le q u a n t ity *

T h e re fo re ,

K>(i x-A e- ) (1/ZX) ^ffle-kTg)

(8)

S u b s t i t u t i n g f o r Z ( x ) from e q u a tio n {5} y i e l d s K*{ i x ^ / i @- } (% £ >

(9 )

I n th e e v e n t t h a t X atom s a r e d e r i v e d fro m a d i s s o c i a t i o n p ro c e s s su ch as Xg(g) * 8X(g)

w here th e Xg I s a t te m p e r a tu r e T(X g) d i f f e r e n t fro m T ( s ) , E ©an b e e x p r e s s e d i n te rm s o f P (X g) b y K.(ir / V ) ( f e )

)i

(1 0 )

th e f a c t o r 2 b e in g I n tr o d u c e d b e c a u se th e mass o f Eg 1® tw ic e t h a t o f X*

8 The e q u i l i b r i u m c o n s ta n t o f t h e r e a c t i o n i s ref­ l a t e d t o th e s t a n d a r d f r e e e n e rg y ch an g e

P ° o f th e r e a c t i o n

X - e - Ap% T s „ {lx - / i e- ) ( l / P xgJ!(TXgB0t/2Ts®e - ) i

«r AF°-OTalnZTlx- / i e«)(l/PXg) (TX2lBx/ 2Ts^e-)!7

(ll)

(12)

Sine® A P °« A H ® -T g 4 S

(IS )

the olectron affinity is expressed by

K gg.) *J.,rw%The l a s t two t e r n s o f E q u a tio n (1 4 ) can be c a l c u ­ l a t e d f o r m ost atom s w ith s u f f i c i e n t a c c u r a c y s i n c e tb s se te rm s a c t u a l l y e x e r t a r e l a t i v e l y s m a ll in f lu e n c e upon th e e q u a tio n a s a w hole*

T h e r e f o r e , i t becom es e v id e n t t h a t th e

-electron a f f i n i t y may b e d e te rm in e d by th e m easurem ent o f the quantities ? ( » ) , i(x”)/i(e~), P(X2 ) and T (X g ).

I t has

b e a n assum ed t h a t i n th e c a s e o f a d ia to m ic g a s , Xg, th e m o le c u le s a r e c o m p le te ly d i s s o c i a t e d i n t o atom s upon com ing i n c o n t a c t w ith th e e q u i lib r iu m s u r f a c e *

On th e o th e r h a n d ,

th e n a t u r e o f E q u a tio n (1 4 ) i s s u c h t h a t th e e q u i lib r iu m c o n s t a n t n e e d n o t b e m easu red v e ry a c c u r a t e l y t o g iv e a r e a ­

sonably a c c u r a t e m easu re o f The e x p e r im e n ta l m ethods w h ich hav e b ee n u s e d by G lo c k le r and C a lv in and by Mayer an d o t h e r s t o d e te rm in e th e e l e c t r o n a f f i n i t y o f th e h a lo g e n s b o th depend upon th e

9 p r e c e d in g t h e o r e t i c a l c o n s i d e r a t i o n s b u t d i f f e r i s th e man­ n e r i n w h ich th e r a t i o i ( x * ) / i(e**) i s d e te rm in e d * f h e s p a c e c h a rg e m ethod u s e d b y G lo c k le r an d G a lv in depend® upon th e w e ll known Langmui r - C h lI d s e q u a tio n

i - CC*/®)^^*

(15)

w here 1 i s th e s p a c e - c h a rg e l i m i t e d c u r r e n t b etw een two e l e c t r o d e s i n te rm s o f a g e o m e tr ic a l c o n s ta n t 0 I s th e g e o m e tr ic a l c o n s ta n t e/m i s th e s p e c i f i c c h a rg e o f the, c a r r i e r s o f th e c u rren t ¥ i s th e p o t e n t i a l d i f f e r e n c e b etw een th e e l e c t r o d e s * t h e e x p e r im e n ta l p ro c e d u re a p p ly in g tb s abo v e r e ­ l a t i o n s h i p in v o lv e s f i r s t d e te r m in in g th e c o n s ta n t 0 9 by t a k in g c u r r e n t - p o t e n t i a l d a t a i n v acu o w h ereb y e l e c tr o n s * f o r w hich th e e/m i s known* a r e t h e s o le c a r r i e r s o f th e c u r ­ re n t#

By t h i s m anner th e v a lu e o f C can be d e te rm in e d *

W ith G known th e e x p e rim e n t i s r e p e a te d w ith a h a lo g e n g a s b etw een th e e l s e trod® * w hereby a d i f f e r e n t v a lu e o f e/m i s o b ta in e d due t o th e f a c t t h a t p a ^ t o f th e c u r r e n t c o n s i s t o f n e g a tiv e io n s* X~»

From th e e f f e c t i v e m ass o f t h e

c a r r i e r s o f th e c u r r e n t i n th e p r e s e n c e o f a h a lo g e n gas* th e r a t i o 1( x ~ ) / i ( e “*) c a n be d e te rm in e d and th e a p p lie d t o E q u a tio n (1 4 ) f o r th e c a l c u l a t i o n o f th e e l e c t r o n a ffin ity *

Mayor an d o t h e r s a p p l i e d th e p r i n c i p l e o f th e mag­ n e t r o n I n th e e x p e r i m e n t a l d e t e r m i n a t i o n o f th e e l e c t r o n a f f i n i t y o f t h e h a lo g e n s *

fh© a p p a r a t u s c o n s i s t e d o f a c y ­

l i n d r i c a l tr ie d © e n c lo s e d i n a s o l e n o i d c o a x i a l w ith i t * E x p e rim e n ts w ere made w hereby* w ith a s m a ll p o s i t i v e p o t e n t ­ i a l o n t h e g r i d an d a s t i l l s m a l l e r p o s i t i v e d r i f t p o t e n t i a l on t h e p l a t e * t h e p la t© c u r r e n t o f th e t r i o d e i n th e p r e s e n c e o f h a lo g e n ato m s w as m e a su re d w ith an d w ith o u t c u r r e n t p a s s ­ in g th r o u g h th e s o le n o id *

W ith o u t th e s o l e n o i d o p e r a t in g *

t h e p la t© c u r r e n t r e p r e s e n t s l i e 4*) s i n c e 1C©"*) i s much g r e a t e r th a n i ( x " ) «

W ith th e s o l e n o i d c u r r e n t f lo w in g s o a s

t o p r o d u c e a c o a x i a l m a g n e tic f i e l d s u f f i c i e n t l y g r e a t t o p r e v e n t e l e c t r o n s fro m r e a c h in g th e p l a te * t h e p l a t e c u r r e n t r e p r e s e n t e d K xf*}*

t h u s t h e r a t i o o f i{ © ~ ) / i U “ ) c o u ld b e

d e te r m in e d an d t h e e l e c t r o n a f f i n i t y o f th© h a lo g e n ato m c a l ­ c u la te d *

IX

O h & p te r XXX

tm

w&a of BmMmTiQM or carbon

The f i r s t m e th o d w h ic h w as u s e d i n a t t e m p t s t o d e ­ te r m i n e e x p e r i m e n t a l l y t h e v a p o r p r e s s u r e o f c a r b o n a s a f u n c t i o n o f t e m p e r a t u r e i n v o lv e d t h e u s e o f t h e c a r b o n a r c # The g ro u n d w o rk f o r t h e s e d e t e r m i n a t i o n s w as l a i d b y V i o l l e { 6 8 } { S 9 } (7 0 ) a n d b y W ilso n ( 7 3 ) ( 7 4 ) *

The f o r m e r r e p o r t e d

t h a t t h e t e m p e r a t u r e o f th e p o s i t i v e c r a t e r o f th e c a r b o n a r c a t a tm o s p h e r ic p r e s s u r e w as c o n s t a n t f o r o p e r a t i n g c u r ­ r e n t s fro m 1 0 t o 2000 a m p e re s#

M o re o v e r h e p o s t u l a t e d t h e

e x i s t e n c e o f th e rm o d y n a m ic e q u i l i b r i u m b e tw e e n c a r b o n v a p o r a t t h e c r a t e r a n d t h e g a s s u r r o u n d i n g th e a r c #

T hus h e c o n ­

c l u d e d t h a t t h e a r c t e m p e r a t u r e a t a tm o s p h e r ic p r e s s u r e r e ­ p r e s e n t e d t h e b o i l i n g p o i n t o f c a rb o n #

W ils o n n o te d t h a t

t h e c a r b o n a r c b u r n e d a t h i g h e r t e m p e r a t u r e s when o p e r a t e d u n d e r h y d ro c a rb o n g a s p r e s s u r e s g r e a t e r th a n a tm o s p h e ric , hummer ( d ) ( 7) w as p r o b a b l y t h e f i r s t t o make a f o r m a l s tu d y o f c r a t e r t e m p e r a t u r e s a s a f u n c t i o n o f g a s p r e s s u r e * b o t h a b o v e a n d b e lo w o n e a tm o s p h e re *

At p re s s u re s

fro m 0*1 t o 1 a tm o s p h e re * Lummer1& t e m p e r a t u r e s v a r i e d fro m K t o 4 2 0 0 ° K*

A t a p r e s s u r e o f tw e n ty - tw o a tm o s ­

p h e r e s a t e m p e r a t u r e o f 7 7 0 0 ° K w as r e c o r d e d #

12 show ed t h a t th e t o t e o f hummer fro m p r e s s u r e s o f 0*1 t o 1*0 a tm o s p h e r e s o b ey ed t h e C l a u s is - C la p e y r o n e q u a t i o n , t e d h e c a l c u l a t e d th e h e a t o f s u b l i m a t i o n o f o a r * b e n fro m t h i s d a t a t o b e 2 8 2 ,4 k c a l a t 300°K*

For p re ssu re s

a b o v e one a tm o s p h e re he o b ta in e d v a l u e s o f L(Q} w h ic h v a r i e d fro m 5 5 t o 1 5 2 ,5 k c a l . I n 1920 K o to , who h ad q u e s tio n e d t h e p u r i t y o f lu m m er’a e l e c t r o d e s an d h e n c e th e e s t a b l i s h m e n t o f s a t i s f a c ­ t o r y e q u i l i b r i u m c o n d i t i o n s , r e p e a t e d hummer*a w ork an d ob­ t a i n e d a v a l u e o f 163*5 k c a l f o r L(G) fro m m e a su re m e n ts a t th a n o n e of

u s i n g d i f f e r e n t k in d s o f

o f v a rio u s p u r l -

t i e s f o r w id e r a n g e o f c u r r e n t snb e le c tro d e a t th e a r c u s in g

t h a t o n ly t b s p r e s s u r e and n o t th e c h e m ic a l c o m p o s itio n o f -the s u r r o u n d in g a tm o s p h e re h a d a n y a p p r e c i ­ a b l e e f f e c t upon c r a t e r te m p e r a t u r e , & t p r e s s u r e s fro m 0*8 t o 6 a tm o s p h e re s th e d a t a o b ta in e d b y Kohn an d G u ck e l c o r r e s p o n d e d v e r y w e l l t o t h e C la u a ls -C la p © y ro n e q u a tio n and y i e l d e d a v a lu e o f L(G) a t

13 t o 138*2 kc& l*

A t p r e s s u r e s o f 0 ,0 6 t o 0*8

th e c u rv e l o g P v s* l / t d ro p p e d o f f s h a r p l y . K oto am i GuckeX a l s o c o n s id e r e d th e q u e s t i o n a s t o th e c a r b o n v a p o r s u r r o u n d in g t h e a r c w as m onaiom ic o r d ia to m ic , a n d a tte m p te d t o c a l c u l a t e s t a t i s t i c a l l y th e e q u i l i b r i u m b e tw e e n c a rb o n an d th e tw o v a r i e t i e s o f v a p o r* t h e i r c a l c u l a t i o n s th e y w ere n o t s u f f i to u t i l i s e th e m u l t i p l i c i t i e s o f th e s t a t e s , d a t a t h a t w ere u s e d w ere n o t a s p r e c i s e a s now known*

From t h e i r c a l c u l a t i o n s th e y o b ta in e d

f o r b { 0 ) e q u a l t o 141*4 k c a l , an d I*(Gg) e q u a l t o 1 8 6 ,0 t e a l *

B e ca u se o f th e a g re e m e n t o f th e f o rm e r v a lu e

w ith t h e i r e x p e r im e n ta l r e s u l t s , K oto and G u ek el c o n c lu d e d v a p o r was p r e p o n d e r a n tly m onatom lc * ig th e d a t a o f K oto and Guo t e l and m aking a c o r r e c t i o n f o r th e h e a t o f f u s i o n o f c a r b o n , c a l c u h e a t o f v a p o r iz a tio n a t 300

& t o b© 147 k c a l*

U sin g th e a r c m ethod a t p r e s s u r e s fro m 0*005 t o 1*50 a tm o s p h e re s , H ls h k e v ic h (5 8 ) o b ta in e d a v a lu e f o r L(C) o f 92 t e a l *

A lso by th e same m ethod T h ie l and H i t t e r (6 3 )

o b ta in e d a lo g P v s l / T c u rv e s i m i l a r I n g e n e r a l a p p e a ra n c e t o t h a t o f K oto and G uekel b u t w h ic h was d i s p l a c e d a p p r o x i­ m a te ly 500 d e g r e e s lo w e r f o r e q u i v a l e n t p r e s s u r e s * o f L ($ ) w h ic h em an ated fro m t h e i r work was 125 k c a l*

The v a lu e

14 I n 1923 W e r te n s te in sa d J e d re s g e w s k i {71} a t t a c k e d t h e h e a t o f s u b lim a tio n p ro b le m fro m a n o th e r a n g l e .

T h ese

a u t h o r s q u e s tio n e d th e p r e s e n c e o f a s t a t e o f therm odynam ic e q u i l i b r i u m i n th e a r c d e t e r m in a t io n s o f L( C} .

A lso th e y

c o n te n d e d t h a t , s i n c e th e n o rm al c r a t e r r a d i a t e s a b o u t one th o u s a n d w a t t s p e r u n i t s u r f a c e , I t i s r a d i a t i o n w h ich p la y s th e e s s e n t i a l r o l e I n p r o d u c in g th e a r c te m p e r a tu r e *

They

t h e r e f o r e a t t r i b u t e d th e v a r i a t i o n o f c r a t e r te m p e r a tu r e s w ith p r e s s u r e a s fo u n d b y th e a r e i n v e s t i g a t o r s a s due t o t h e f a c t t h a t th e p o t e n t i a l d ro p i n th e a r c i n c r e a s e d w ith in c re a s in g p r e s s u r e . F o r th e s e r e a s o n s t h e r e f o r e , W e r te n s te in and J e d r e s ie w s k i m o d th e m ethod by w h ich L& ngim ir (3 8 ) had deter** m ined th e h e a t o f v a p o r i s a t i o n o f tu n g s te n *

T h is m ethod i n ­

v o lv e d m e a s u rin g th e tim e r a t e o f w e ig h t l o s s i n vacuum o f a f i l a m e n t o f th e m a t e r i a l u n d e r c o n s i d e r a t i o n .

I n th e tem ­

p e r a t u r e ra n g e 2 8 0 0 ° t o 5 5 0 0 ° K th e e x p e r im e n ta l v a lu e ob­ t a i n e d b y t h e s e i n v e s t i g a t o r s c o r r e s p o n d e d w e ll t o th e Cl a u s i s - Cla p s y r on r e l a t i o n w hich y i e l d e d a v a lu e o f 215 k c a l • f o r 140} a t 300°K*

E x t r a p o l a t i o n o f t h e i r lo g ? v s l / T

c u rv e s t o one a tm o s p h e re gave th e b o i l i n g p o i n t o f c a rb o n ad 5100® E* The n e x t e x p e r im e n ta l d e te r m in a tio n o f th e h e a t o f s u b lim a tio n o f c a rb o n was r e p o r t e d i n 1933 by M a rs h a ll and H o rto n (4 6 ) who d e te rm in e d v a p o r p r e s s u r e from th e rat©

15 o f l o s s t o w e ig h t o f c a rb o n r i n g s h e a te d by h ig h f r e q u e n c y i n d u c t i o n i n a vacuum* Upon th e b a s i s o f c a l c u l a t i o n s b y Vaughn and E is tia k o w s k y ( 68) w h ich w i l l be ta k e n up l a t e r * th e y a s mum** e d t h a t t o th e te m p e r a tu r e ra n g e 2 3 0 0 ° K t o 2800° K n i n e t y tw o t o n i n e t y - s i x p e r c e n t o f th e c a rb o n e v a p o r a tin g was m onatom lc* an d fo u n d a v a lu e f o r L(C) o f 1?7 k c a l*

E x tr a ­

p o l a t i o n o f t h e i r d a t a w h ile ta k in g a c c o u n t o f th e Gg fo rm e d a t th e h i g h e r te m p e r a tu r e s g av e f a i r l y c lo s e a g r e e ­ m ent w ith th e d a t a o f Koim and Q uekel above 4 2 0 0 ° &* R e c e n t work t o t h i s f i e l d I s t h a t o f Rib&ud an d Begue {57} who h e a te d g r a p h i t e c y l i n d e r s I n a h ig h f r e q u e n ­ cy f u r n a c e i n a n a tm o sp h e re o f a rg o n a t p r e s s u r e s fro m 30 t o 700- m i* u n t i l v a p o r i s a t i o n o c c u rre d *

Two m ethods o f f i n d ­

in g th e te m p e r a tu r e o f s u b lim a tio n w ere u sed *

One in v o lv e d

h e a t i n g g r a d u a l l y t o 2 3 0 0 ° E th e n i n c r e a s i n g pow er consump­ t i o n above t h a t n e c e s s a r y f o r s u b lim a tio n an d p l o t t i n g a tim e - te m p e r a tu r e c u rv e *

In e a c h c a s e a f l a t p o r t i o n was

n o te d on t h e c u rv e and t h i s was ta k e n a s th e te m p e r a tu r e o f s u b lim a tio n a t th e p r e s s u r e o f a rg o n i n th e a p p a r a tu s *

The

o t h e r m ethod c o n s i s t e d o f m e a s u rin g th e te m p e r a tu r e o f o p e r a t i o n f o r d i f f e r e n t v a lu e s o f pow er In p u t*

A f l a t p o r­

t i o n on th e 'te m p e r a tu r e - in p u t c u rv e gave th e te m p e r a tu r e o f s u b lim a tio n *

R e s u lts from th e two d i f f e r e n t m ethods o f

16 s u b li m a t io n a s a f u n c t i o n o f p r e s s u r e w ere c o n s i s t ­ e n t an d g av e r i s e t o an e m p i r i c a l r e l a t i o n su c h t h a t S { % ) - 3484 4 5 ,3 7 p ~ 0 .0 1 1 8 ps w here p i s e x p r e s s e d i n c e n t i m e t e r s o f Eg*

The correspond**

in g v a lu e o f 1(C ) i s 140 ko&l * I n 1948 B rew er, 01 l i e s and J e n k in s (IB ) r e p o r t e d th e h e a t o f s u b lim a tio n o f g r a p h i t e d e te rm in e d b y a d i r e c t d e t e r m ln a t io n o f th e t o t a l v a p o r p r e s s u r e o f g r a p h i t e by an e q u i l i b r i u m e f f u s i o n m ethod and by th e d e te r m in a tio n o f th e p a r t i a l p r e s s u r e o f Cg(g a s ) i n e q u i l i b r i u m w ith g r a p h ite * They fo u n d th e h e a t o f s u b lim a tio n o f g r a p h i t e t o 0(g ) t o b e 170 k e a l* p e r m ole a t 0° K*

The h e a t o f s u b lim a tio n o f

g r a p h i t e t o 0 g ( g ) I s fo u n d t o be 253 k c a l* p e r mol©*

The

c o e f f i c i e n t o f c a rb o n g a s on g r a p h i t e a t h ig h i s fo u n d t o b e a b o u t 0*3 an d v a p o r is e d c a rb o n g as i s shown to be in. th e

g ro u n d e l e c t r o n i c s t a t e ,

lo n g (4 0 ) d i s a g r e e s w ith B rew er ©i a l who g e t from t h e i r e q u i l i b r i u m e f f u s i o n m ethod a v a lu e o f 170 k a a l f o r L (C ) on th e f o llo w in g b a s i s s 1*

A l l o t h e r e q u i l i b r i u m te m p e r a tu r e and p r e s s u r e mea­

su re m e n ts (’T h ie l and H i t t e r ; B a s s e t; H ibaud and Begue) su p ­ p o r t th e lo w e r v a lu e o f 125 k c a l . 2*

Two In d e p e n d e n t I n v e s t i g a t o r s ( B a s s e t (1 3 ) and

S t e i n l e ( 6 0 ) ) fo u n d th e t r i p l e p o i n t o f c a rb o n t o be a t

17 100 a tm o s p h e r e s * c o n c lu s io n s *

B o th h a v e p h o to g r a p h ic e v id e n c e f o r t h e i r

A c c o rd in g t o B rew er t h e v a p o r p r e s s u r e i s 100

a tm o s p h e r e s a b o v e 6 0 0 0 ° JU

I M s p la c e d th e m e ltin g p o in t

o f g r a p h i t e a t a n im p o s s i b l e f i g u r e , w e l l a b o v e th o s e o f t h e refractory m e t a l c a r b i d e s * w h e re a s i t

i s known t h a t g r a p h ! t e

c a n b e f u s e d i n a c r u c i b l e o f t a n ta l u m c a r b i d e (su p # 4 1 5 0 ° K). I n a d d i t i o n t o t h i s s e v e r a l i n v e s t i g a t o r s h a v e g iv e n a p p ro x i­ m a te ly the same v a l u e f o r t h e m e l t i n g p o i n t o f g r a p h i t e an d i t w ould seem s t r a n g e t h a t a l l o f th em w o u ld v a r y b y ap p ro x i­ m a te ly t h e same v a l u e i f t h e B rew er v a lu e i s c o r r e c t * 3*

I f t h e v a p o r p r e s s u r e o f g r a p h i t e r e a c h e s o n e a tm o s­

p h e r e a t 4 € 3 0 ° K a s p r o p o s e d b y B rew er* i t i s s u r p r i s i n g t h a t th e te m p e ra tu re s r e p o r te d f o r th e p o s i t i v e c r a t e r o f th e c a r b o n a r c * w h ic h a r e g e n e r a l l y r e g a r d e d t o be l i m i t e d b y t h e v a p o r p r e s s u r e * a r e n e v e r s e n s i b l y ab o v e 4 0 0 0 ° K** even u n d er e le v a te d p re ssu re * 4*

A p a r t fro m th e a b s o l u t e te m p e r a tu r e m e asu rem e n ts*

M o tt {B I) h a s d e te r m in e d th e r e l a t i v e v o l a t i l i t i e s o f a num­ b e r o f s u b s t a n c e s fey a v a r i e t y o f m eth o d s*

H is p la c e m e n t o f

c a r b o n o f f e r s s u p p o r t t o t h e m e a su re m e n t o f B a s s e t an d o f T h i e l an d R i t t e r * b u t i s n o t i n harm ony w ith th o s e o f B rew er e t a l* From t h i s e v id e n c e Long c o n c lu d e s t h a t g r a p h i t e p o s s e s s e s a m uch h i g h e r v a p o r p r e s s u r e an d c o n s e q u e n tly

lo w e r h e a t of* s u b lim a tio n th a n t h a t a f f i r m e d b y B rew er* He a l e e s t a t e # 41I t i s r e l e v a n t t o n o te t h a t th e s e a u th o r s i n t h e i r e x p e r im e n ts w ith r e p l a c e a b l e g r a p h i t e tube® fo u n d t h a t r a p i d v o l a t i l i s a t i o n o c c u r r e d w h ich l i m i t e d th e l i f e o f th e tu b e # * 1® T h is o b s e r v a t i o n i s s c a r c e l y c o m p a tib le w ith t h e i r own te m p e r a t u r e - p r e s s u r e r e l a t i o n * w hich i n a l l c a s e s ne­ c e s s i t a t e s p r e s s u r e w e ll below 0*1 mm» a t th e te m p e r a tu r e o f t h e i r e x p e rim e n ts * S im p so n , T horn and W inslow (IS ) o b ta in e d d a t a f o r t h e v a p o r p r e s s u r e and th e h e a t o f s u b lim a tio n o f ca rb o n * The d a t a was o b ta in e d by c o l l e c t i n g g r a p h i t e v a p o r on a q u a r t# t a r g e t p la c e d abo v e a h e a te d g r a p h i t e c y lin d e r® m easu rem en ts e x te n d e d fro m 2 3 0 0 ° K to 2 500° 1U

The

The h e a t o f

s u b lim a tio n w as o b ta in e d b y m e a su rin g th© r a t e o f decom posi­ t i o n o f th e v a p o r on th e t a r g e t w ith th e a i d o f an o p t i c a l p y ro m e te r*

The v a p o r p r e s s u r e was m easu red b y w e ig h in g th e

h e a v ie r d e p o s its *

The v a p o r p r e s s u r e was u se d to make a n

In d e p e n d e n t c a l c u l a t i o n o f th e h e a t o f s u b lim a tio n w ith th® a i d o f d a t a f o r th e s p e c i f i c h e a t o f s o l i d g ra p h ite ®

In

t h i s m anner th e y o b ta in e d 174 S c e a l/ m ole f o r th e h e a t o f s u b lim a tio n t o t h e m onatom ic fo rm a n d 7*7 x 10

f o r th e

vapor p ressu re* From th e v a p o r p r e s s u r e and from s p e c tr o s c o p i c d a t a , one c a n e u lc u la t© th e e n tr o p y o f th e monato-mic gas i n

l e a l ralaM -en # .*

T h i s , t o g e t h e r w i t h t h e e n t r o p y o f th® s o l i d one to c a l c u l a t e fo rm a t 0°

r e l a t i o n g iv in g t h e h e a t o f s u b l i m a t i o n a t a b s o l u t e ae ro .# o la

55 /

H ln f* /&BlrM *RlnQ

Z iC * T * » ln I- £

1

H lnl

J

d f + V fJ^ G p d f}

(1 )

w here p i s th e- v a p o r p r e s s u r e i n d y n e s / em^ f i s th e te m p e r a tu r e i n d eg ree© a b s o l u t e M i s t h e a to m ic w e ig h t o f c a rb o n {12*01} ^ i s th e p a r t i t i o n f u n c tio n k i s t h e B o ltsm a n n c o n s t a n t b i s P lan c k * a c o n s t a n t Kq i s 4 v eg a d r o r $ num ber Op i s th e h e a t c a p a c i t y a t c o n s t a n t p r e s s u r e o f

When S q u a tio n (1 ) i s d e r iv e d * a c o m p le te e x p r e s s io n f o r th e e n tr o p y o f th® v a p o r s h o u ld i n c l u d e a te rm r i s i n g fro m th e e l e c t r o n i c p a r t i t i o n f u n c tio n * th e e n t r o p y o f m ix­ in g o f th e two c a rb o n i s o t o p e s and th e e n t r o p y due t o t h e n u c l e a r s p in o f C*kS»

"The d i s p o s i t i o n o f t h e s e l a s t tw o term s

i s made v i a argum ent© u s e d b y E p s te in (3 )*

W ith th e a v a i l ­

a b l e s p e c i f i c h e a t d a ta * th© e n tr o p y o f th e s o l i d s h o u ld a l s o

e @ n ta f» t h e s e m ix in g an d s p i n t e r n s , s o t h a t t h e y c a n c e l o u t in

E q u a ti o n ( 1 ) , The a r g u m e n ts { u s e d b y £ p s t e i n w ith r e g a r d t o

m ix e d c r y s t a l s , l * e . , w i t h r e g a r d t o t h e e n t r o p y o f m ix in g ) i s t h a t th e e n tro p y c o n s ta n t t h e o r e t i c a l l y i s a e r o 5 t h a t l a * t h e r e s h o u l d h e o n ly on© m o d i f i c a t i o n o f t h e c r y s t a l w h ic h i s i n th e rm o d y n a m ic e q u i l i b r i u m a t t h e a e r o p o i n t * N e v e rth e le s s th e r a t e s o f r e a c tio n an d th e e n e rg y d if f e r e n c e s b e tw e e n m o d i f i c a t i o n s a r e s o s m a l l t h a t i n m o s t e x p e r i m e n ts done i n a f i n i t e

tim e t h e r e w i l l a p p e a r a n a p p a r e n t " z e r o

p o in t e n tro p y ” (9 ) *

T h is a rg u m e n t i s a p p l i e d h e r e t o b o t h

t h e e n t r o p y o f m ix in g a n d t h e s p i n e n t r o p y o f C ^ *

S in c e

i t a p p e a r e d l i k e l y t h a t a " z e r o p o i n t e n t r o p y ” w o u ld o c c u r f o r th e s o l i d , i t i s a r b i t r a r i l y

d e c id e d t o s e t i t e q u a l t o

t h e m ix in g a n d s p i n c o n t r i b u t i o n s t o t h e e n t r o p y o f t h e v a p o r* The e l e c t r o n i c p a r t i t i o n f u n c t i o n , f t, i s g i v e n b y

q, «> £ . p je

€ t/k T

(2 J

i n w h ic h p ( i ) i s t h e d e g e n e r a c y o f t h e 1t h s t a t e 6. ( 1} i s

t h e e n e r g y o f th e i t h

s ta te *

W ith t h e r e q u i r e d d a t a fro m S h e n s to n e {5 0 ) t h e c o n t r i b u t i o n o f e a c h e n e r g y s t a t e t o t h e p a r t i t i o n f u n c t i o n c a n h e eal*» c u la te d *

E x a m in a tio n o f t h e s e c a l c u l a t i o n s

show s t h a t o v e r

a t e m p e r a t u r e r a n g e fro m 1 8 5 0 ° & t o 2 5 0 0 ° K l o g Q i s a

c o n s t a n t t o bh© n um ber o f f i g u r e s u se d * Sim pson* T h o rn a n d W inslow (1 2 ) c a r r i e d o u t t h e I n t e g r a t i o n s i n E q u a tio n ( 1 ) w ith a p l a n i m e t e r *

U sin g t h e

b e s t a v a i l a b l e d a t a £4 1 ) ( 2 1 ) an d e v a l u a t i n g th e c o n s t a n t t e r n s , th e r e l a t i o n s h i p b e tw e e n t h e v a p o r p r e s s u r e , h e a t o f s u b l i m a t i o n a n d te m p e r a tu r e mmj b e e x p r e s s e d a s f o llo w s i AH®+2963 l o g P * ^ '".sM" 'R f *

_ 1 5 .5 4 6 - 0 .3 3 9 3 l o g T - 2 . 1 9 x ICT^T

(3)

w h ere p I s e x p r e s s e d I n d y n e s p e r ea®» AH§ a n d B a r e b o t h e x p r e s s e d i n te rm s o f th e c a l o r i e u n i t * T a b le I I I - l show s t h e v a p o r p r e s s u r e o f c a r b o n f o r v a l u e s o f 136 a n d 170 k c a l* /m o le f o r t h e h e a t o f s u b li m a t io n o f c a rb o n *

I n 1932 Vaughn an d K is tla k o w s k y ( 8 3 ) c a l c u l a t e d t h e h e a t o f s u b l i m a t i o n o f c a r b o n i n t o m onatom ic v a p o r b y c o n s i d e r a t i o n o f th e e n e r g y c y c l e :

CO------- > C(g) 0 (a )

* 0

* | £ % --------------------

o -------* |0g G^e y

-»c(g)

The h e a t o f c o m b u s tio n o f c a r b o n an d t h e d i s s o c i a t i o n e n e rg y o f oxygen a r e a c c u r a t e l y known*

U sin g a s p e c t r o s c o p i c

v a l u e o f 10*35 e*v* f o r t h e d i s s o c i a t i o n e n e r g y o f c a r b o n

m o n o x id e r e s u l t e d i s a ? a lu ® o f 1 5 S .5 k o a l . p e r m o le f o r

h(C) a t 0 ° K. By ta k in g l i k e l y f i g u r e s f o r t h e h e a t o f d i s s o e fac­ t i o n o f t h e Gg m o le c u le fro m s p e c t r o g r a p h i c d a t a on c a r b o n , 5 * 6 load 7 * 0 e * v * , Vaughn and K is tia k o w a k y a l s o c a l c u l a t e d s t a t i s t i c a l l y t h e e q u i l i b r i u m b e tw e e n m onatom ie an d d ia to m ic c a r b o n v a p o r and f o u n d L (C ) a t 0 ° s t o b e 161 o r 176 k c a l* a n d L (C g) t o b e 105 an d 189 ke& l* r e s p e c t i v e l y f o r th e 5*5 a n d 7 * 0 e* v * d i s s o c i a t i o n e n e r g i e s *

T h e ir c a lc u la tio n s

a l s o show ed t h a t a t t e m p e r a t u r e s fro m 4 1 5 0 to - 4 7 0 0 ° K, c a r ­ b o n v a p o r I s p r e p o n d e r a n t l y d ia to m ic w h e re a s a t t e m p e r a t u r e s n e a r 2 5 0 0 ° K t h e g a s I s a lm o s t c o m p le t e ly m onatom ie* The u s e o f s p e c t r o g r a p h i c e v i d e n c e f o r th erm o ch em ­ i c a l c a l c u l a t i o n s o f 1 (0 } b y Vaughn a n d X ia tia k o w s k y p r e ­ c i p i t a t e d a n a v a la n c h e o f p a p e r s i n t h e f o l l o w i n g y e a r s b y v a r i o u s i n v e s t i g a t o r s who f a v o r e d d i f f e r e n t i n t e r p r e t a t i o n s o f t h e b a n d s p e c tr u m o f c a r b o n an d h e n c e o b t a i n e d d i f f e r e n t c a l c u l a t e d v a l u e s f o r L (G )•

One o f th e m ore c o m p re h e n s iv e

o f t h e s e c o n t r i b u t i o n s w as made b y Go I d f i n g e r an d Jeunehcm ne (2 9 ) who p r e s e n t e d c a l c u l a t e d v a p o r p r e s s u r e c u r v e s u s i n g t h r e e o f th e f o u r c o n t r o v e r s i a l s p e c t r o s c o p i c v a l u e s f o r t h e d i s s o c i a t i o n e n e r g y o f c a r b o n m o n o x id e , 1 1 * 0 6 , 9*10 a n d 8*58 e* v *

The v a l u e s o f L (G ) o b t a i n e d fro m t h e s e v a l u e s

w ere 1 6 8 * 8, 123 * 6 and 107 * 2 k c a l . r e s p e c t i v e l y *

fab1* III-!

Vapor Pressure of Garbon as a Function of f eiapera ture for L(G) equal to 156 and 170 keal* pea? Mole f

(«K) 1SS0 1875 1900 1928 1280 197 8 2000 20 2 5 2050 2075 2100 2128 2150 2175 2200 225 0

mm 255 0 2400 2480 250 0

le g

UQ)

p (atm) * 186

-8 * 0 2 5 - 7 *008 -7 * 5 9 7 -7 * 3 9 1 -7 * 1 9 2 —6*997

-6*aos

-6 * 6 2 2 —6 * 4 4 5 —8*265 — 6*094 -5 * 9 2 7 -5 * 7 6 3 -5 * 6 0 2 -5 * 4 4 6 -5 * 1 4 5 —4*854 - 4 .5 7 7 -4 * 5 1 3 -4 * 0 5 9 -3 * 8 1 5

lo g p (atm) L (0 ) * 170 -1 2 * 0 4 1 -1 1 * 7 7 1 -11 *508 -1 1 * 2 5 1 - 11.002 -1 0 * 7 5 9 — 10*525 —10 *291 -1 0 * 0 6 7 - 9.84® - 9*632 - 9 .4 2 3 - 9 .2 1 8 — 9 *018 - 8*823 - 8*445 - 8*084 - 7 .7 5 9 - 7 .4 0 9 - 7 .0 9 1 - 6*787

m C o m p lete a g re e m e n t h a s n o t b e e n r e a c h e d c o n c e r n in g t h e d i s s o c i a t i o n e n e r g y o f c a rb o n m onoxide*

The m o st w id e ly

a c c e p te d v a lu e i s t h a t o f 9*14 e *v* p ro p o s e d b y H e r ts b e rg * T h in v a l u e l e a d s t o a v a l u e o f 124*4 t e a l * f o r 1 ( 0 ) * I n 1946 Long an d H o r r is h {41} made a c r i t i c a l r e ­ v ie w o f th e c o n t r o v e r s y w h ic h e x i s t s b etw e en th e f i g u r e s 125 a n d 170 t e a 1 / g -a to m f o r t h e l a t e n t h e a t o f s u b lim a tio n o f c a rb o n i n t o m onatom ic v a p o r i n th e g ro u n d s t a t e *

T h is c o n -

t r o v e r s y o r i g i n a t e s l a r g e l y fro m th e n e g l e c t t o t a k e i n t o c o n s i d e r a t i o n t h e e n e rg y r e q u i r e d t o r a i s e th e c a rb o n ato m s fro m th e g ro u n d (% } s t a t e t o t h e lo w e s t t e t r a v a l e n t (^ S } e l e c t r o n i c c o n f i g u r a t i o n c o r r e s p o n d in g t o t h a t i n w h ich i t i s n o r m a lly fo u n d i n c h e m ic a l c o m b in a tio n *

C o n s id e r a ti o n o f

th e e n e r g i e s o f re m o v a l o f a h y d ro g e n atom fro m m ethane and e th a n e m o le c u le s a n d o f t h e e n e r g i e s o f r e o r g a n i z a t i o n o f t h e r e s u l t i n g r a d i c a l l e a d s t o th e f i g u r e 190 t e a l f o r L{2}# f e e h e a t o f s u b li m a t io n I n t o f r e e a to m s i n t h e ?S s t a t e * T h is I n t u r n l e a d s t o a s a t i s f a c t o r y a n d unam biguous a s s i g n ­ m ent o f v a l u e s t o bond e n e r g i e s {as d i s t i n c t fro m d i s s o c i a ­ t i o n e n e r g i e s ) w h ic h c a n now b e e x p r e s s e d w ith an u n c e r t a i n ­ t y o f n o t m ore th a n a few k i l o c a l o r i e s , 46I n t h e l i g h t o f t h e v a le n c y d i s t i n c t i o n t h e r e re m a in s no sound e v id e n c e t o m ain ­ t a i n th e h i g h e r v a lu e p u t f o rw a r d f o r L{1) and 125 t e a l I© u n q u e s tio n a b l y o f t h e r i g h t o r d e r E a r l y i n 1947 H ag stru m (3Q) p o in te d o u t t h a t t h e

25 th r e e c o n tr o v e r s ia l v a lu e s f o r th e d is s o c ia tio n e n e rg y o f CO a l l

d i s a g r e e d w i t h t h e v a lu e o f 9*6 e .v * a s o b t a i n e d

fro m e l e c t r o n c o l l i s i o n e x p e r im e n ts *

T h is v a l u e r e s t s u po n

a body o f d a t a o b t a i n e d b y m e th o d s w h ich p ro d u c e e x c e l l e n t a g r e e m e n t w i t h w e l l e s t a b l i s h e d r e s u l t s fro m b an d s p e c t r a f o r Hg* Hg* 1 0 a n d 0g«

T hus h e s u g g e s te d t h a t a r e c o n c i l i a ­

t i o n o f t h e c o n f l i c t i n g p o s i t i o n s o f th e s p e c t r o s c o p i c v a l u e s f o r 60 was i n o r d e r * Some m o n th s l a t e r H ag stru m 79? (1 9 4 8 ). ** ------

19*

P* M. Doty and J » 1 , l a y e r , X* Ohm* Fhys. 1 2 , 325 (1944}« ~ —~ ~

20.

J . Duchesne, P, G o ld fin g er and Rosen* Mature* 159. 129 (1 9 4 7 ). ---------- -----

21.

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0 . G lo c k le r, Phys. Rev*, 41, 685 (1932).

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G. G lo c k le r, Phya* Bey,*. 45, 111 (1934).

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G* G lo c k le r, J* Chera. Phya*, 16* 842 (1948)*

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G* G lo c k le r and

M* C alv in , £ • Ohera. Fhys. , 3 , 771 {1957}.

27*

G. G lo c k le r and

M* C a lv in , X. Ghem. Fhys. , 4 , 492

(1938).

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G, G lo c k le r and X* W* S a u s v llle , X. Blectrochem * S o c ., 9 5 , 282 (1949)•

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H* P* H agstrum ,

Phya* Rev** 7 1 , 377 (1947)#

31*

H. D* Hagatmm,

Fhys * Rev*, 7 1 , 947 (1947)*

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E* A* H y lle ra s ,

g e lt* Phya** 60, 624 (1 9 4 0 ).

90 33.

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6 3 . 291 (1 9 3 0 ).

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M. M etlay an d 0 . ®. K im b a ll, £ . Chem. Phya* . 1 6 , 774 (194®)*

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J ,

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J .

E . M ayer, J . Chem. P h y a ., 8 , 282

100:

82 « L* P au lln g i? 88*

SSE?W *

285 {192? } •

W* 0* JtaMJb 2£K8t* Farads So©*, 31, 734 {1933),

84* a* Fice&rdI, lelt* Phya*, 43, 899 (1927)* ■53* a# PAco&rdi and 1* Holla, lend* Lino* (6), 5, 346 (1927)* 58# K* Pitzar, Chem* lev*, 27, 39 (1940). 37% 0* Hibaud and 1* Begue, Comptea renduas 221* 73 {1945)* 38* E* Rtshkevlch, Zelt* Elektrochem** 31, 54 (1925)* 59# A* 0* Shenstone, Phya* Rev,, 72* 411 {1947)* 60* H* Steinle, Eeita* j% an^ew, MineraloKi®* 2, 344 (1940), 61*

0, P, Stevenson, J» Chem* Phya** 10, 291 (1942),

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?* P* Sutton and J* I* Mayor, J*. Chem* Phya** 3* 20 (1935) * * ~

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J* 1* Van fleck, £* Chem* fhys** 2, 20 (1934),

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W* E* faughn and 0* B* Eistiakcmsky, Fhys* lev** 40, 457 (1932)•

67* 0* T* fier and J. £. Mayer, £• Chem, Fhys,a 12, 28 (1944), 68*

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Comptes rendua* 115* 1273 (1892)*

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174 (1 8 9 5 )