I iD-AI137 270 CORDSORPTION CHEMIISTRY OF H2 FIND C2N2 ON PT(ii): A i/iCOMMION INTERMEDIAITE I.. (U) CALIFORNIA UNIV IRVINE DEPTOF CHEMISTRY J R KINGSLEY ET RL. 1979 TR-9

UNLSIID NOi-7--68FG74 N

EhEE EEEE EEE

-. - .~-.. .- ,-. -. 7 7 -

36

19.1~ 2.1

L-8-1

I~hI~ 11 1 1.6II

MICROCOPY RESOLUTION TEST CHARTI NATIONAL BUREA OF STANOARDS-963-A

SEC JR:" Z'ASS ZN 09 T- AAS **.o :eta ,,*,

REPORT DOCUmENTAT ION PAGE EZ:sc ;

4. ITI-,c and au1~e -YO -;r ME -:t i,-

Coadsornticon Chzmistry of HI- and 2~ n ?: t 1):-A Common :ntermediate in the Hvydrnyrena~lion of

LOyano!-en and the rDehydrogenat on ci: E--yla 'Ac 3

a2min e on t2) ______

J 3.. Kinnsley, David Da. Iiqren ano %'j:Jon C. Hernirnger

i, 0

ERPnAMN -AA ZAw N .,ME AN AZINS - =C 45..

-A Department of C-.emistry*zL ni'ers-Ity of California

:'-iie,_.a4f,:-rnjia 92717 __________

o~ 'lval es earch7IE De:arr-mert of tne lavv '3 Z A3

3r, j uj ,/S - "r

Cfceof:avai '%esearclh C, a SAes~lern 1>oioral Oflfic3_______1030 E.3^reen Street

'r '~9T~ of 1.his Ropor:;'

Aooroved for j-,ublic release: d iStICr4,b t o n u n 1 -je

17. 017SU'iCM STATE)WEN (of !he abstract .n'trod irt B!ock 'I Vj!tfo,q, t" R .por,;

.o beobi di Surface Science r

*19. KE~Y WORDS (:flrnu.ma *n ?@v.t.# old# it '2*Co44&tY wd !dAl.'/ 3v b)ZCA nucf'CyarogenHydrocenEthylenediamnine?lati nunM) ' /

23. ASS7 A'. 'Cantirtwo on- reers~e old* . pa o4)' Ar~d d.iaolfY -v 01cce mj',9

Z~~~ -'Fhe azdsor:)tion of 2N on Pt:' 1 res.-i-s 'n two ~ . nsae',The~ state, ~ -26 zK, is due to '.ne osr:z ~ze~e/asre

I.E C -zN 2 7he,'- stace, m7; 7310K, m~ay tta 'te to the o ~ - -; :CI Tro)u.s or The ecrcsio-'o an ixtended .

LA. aH I2 rs~1s a s jr a ce ai~r ric ae:: : n 7Cz1'2 at ,2..ecosin : .

D O 1473 z66N ' I c 61 S i

% I.

DISCLAIMER NOTICE

THIS DOCUMENT IS BEST QUALITYPRACTICABLE. THE COPY FURNISHEDTO OTIC CONTAINED A SIGNIFICANTNUMBER OF PAGES WHICH DO NOTREPRODUCE LEGIBLY.

20. ABST?.ACT kcor:inued)

-i -Dehydroenation of ethylene-1--danine SncWS tha: 'he amlie ' ~lrczers are ecefirst in this process followed at 4210K by the removal Of :ne hIydrogens --rom th"ecarbons liberating C12ihrlas the final product. 4

4*4P

OFFICE OF NAV;AL RESE.ARCH

* Contract TCOO14-79-C-06'S

Technical Report No. 9

Coadsorption Chemistry of,; H, and C41- on Ptf1l1): A

Common intermediate in the Hydrogenation of Cyanogen

and the Dehydrogenation of Ethylenedia-1ine on tl)

by

J-R. Kingsley, David Dahigren

and John C. Heniminser

To be Published

in

Surface Science

University of California, IrvineDepartment of ChemistryIrvine, California 92717

Reproduction in whole or in 'part is permitted forany purpose o-f the United States Government

*This document has heen approved for public releaseand sale; its distribution is unlimnited

Coadsorption Chemistry of H2 and C2 N2 on Pt(!1: A Comm on

Intermediate in the Hvdrogenati.on of Cyanoen 3nd the

Dehydrogenation of Et.hvlenediam.ne on Pt2" l).

J.R. Kingsley, David Dahlgren and John C. Hemminger

Department of Chemistry

University of California, Irvine

Irvine, California 92717

Abstract

The adsorption of C2 N2 on Pt(ll!) results in two descr-utin

states (ad). The a state, Tma x = 368K, is due to the desorption

of molecularly adsorbed C2 N2. The - state, Tmax = 730K, may be

due to the recombination of adsorbed CN groups or the deccm.z-

sition of an extended (CN)x polymer. Coadsorption of H2 and C N

results in a surface nitrene which decomposes to give back H2 Rnd

C2N2 at 430K. Decomposition of ethylenediamine results in the

same species. Dehydrogenation of ethylene-d4 -diamine shows that

the amine hydrogens are removed first in this process followed at

430K by the removal of the hydrogens from the carbons liberating

C2 N2 as the final product.

Copy available to DTIC does notpormit fully legible reproduadon

I ' "' :" .'" " " ' " ', -"**' . * . * . .'i?'-: iZ , :i ' ""

2

1. INTRODUCTION

Recently there have been several studies of the bonding and

chemistry of organic cyanides on the surfaces of a varie-v of

single crystal metals; CH 3CN (10) , CH 3NC (10) , HCN (2,3) , C2N2

(1,2,4-6,10,12-14) , and C 146 (11) have been the objects of

studies on various surfaces of Pt, Ni, and Cu.

The oxidation of C2N2 has been studied on Cu4!' The thermal

chemistry of C 2 has been studied previous-yon ?'o0 I4 y,

14) , Pt(110) (2,6), Pt(11 ) (;2) and a steppoed Pt su:rface wit-

Pt(1ll) terraces (5) . Only C 2N2 is observed as a desorotion

product from Pt surfaces. in all of these cases three descro::cn

states are observed (a, all 32 ) . The a state desorbs in t-e

temperature range of 370 K (for the Pt(1116) to 460 K (for the

Pt(1l0) surface). The a1 state desorbs in the range ES0 K - 690

K. The 82 state desorbs in the range 750 K to above 3CO K. The

present interpretation of the a state is that it is due to mole-

cularly adsorbed cyanogen. Two interpretations of :-e 3 states

have been put forward. Lambert, et. a!. (2) have sucoeste= tha-

the S states are due to the recombination of CN oroups, while

Netzer, et. al. (4) have proposed the existence of a paracyanogen

like overlayer.

In this oaper we describe the chemistry of C N2 , the cca_-

sorption chemistry of H2 and C2N2, and the deczmpos:-ion of

ethylenediamine on Pt(l1l).

- -, ,- -%, - ._ - .. - .-. ,. . ..... , . .... .. . .

3

2. EXPERIMENTAL

All experiments were performed in a stainless steel ultra-

high vacuum chamber with a base pressure of less than 1 X 10-

torr. The system is equipped with four-grid LEZD optics, a UT:

100C quadrupole mass spectrometer and an argon ion gun. Auger

analysis was performed by using the LEED optics as a retarding

field analyzer. The mass spectrometer is multiolexel with an 13M

Personal Computer, which performs at su::ic:en - sed to allow

the moni-oring of sixteen seoarate masses and the zrvyszal -eer-

ature every second. The Intel 3037 mah eatics coorocesso:

used to aid in signal averaging of the mass and temperature

signals and in evaluating a fourth order polynomia! to correct

for non-linearities in the thermocouole voltage. The co=pu-er

has also been set up to take Auger spectra and to produce hard-

copy output on a dot matrix printer of both the Auger and thermal

desorption spectra.2

The crystal used has approximately 0.5 cm surface area on

both sides and is 1.5 mm thick. The crystal is spat-welded to a

platinum wire which is attached between two copper rods. The

crystal is resistively heated by a dc current through the copper

rods and the spot welded Pt wire. The temperature ramp is forced

to be linear by a simple feedback circuit which senses the therm-

ocouple voltage and controls the dc power supply.

The crystal temperature is monitored by a chrcme!-alume

thermocouple spot-welded to the edge of the crystal. The Cocoer

rods are also in thermal contact throuch saoon*ra washers wi:n a

.... o . h ...... ,.... . -.

4

reservoir of liquid nitrogen w .hich allows cooling of the crystal

to 100 K.

All Idas exposures were perfor-med in the pressure range of I X

lo- torr to 5 X 10-8 torr. Pressures were read directl; fro

the ion gauge without correction for sensitiv:ity relative to 1

The reagents in this experiment were _,sed without;" further- our:::-

cation before introduction to the vac,-u svszem. The et"Vlene-

diamine and the ethylene-d 4 -diamina, w*.--h are q-uids a: r,: c

temoerature, were degassed by severa rcl---

The scurCes and stated rouririe4-s of:ereacen-s were

teru~,M-atheson - purity 99.5%, (2 Ca_:e, >.e -z

98.5%, (3) ethy-enedianine, F~se -L s-5% 94eK~

amnine, MSD - purity 99.5% .'ot ; i5E3 w-

*The P t(111) crystal was =:eaned bysanzar4 tec~iniq.:s:::

bomba rd4en t, annea ling and ox-,zan trea:=ents. Ca3re was :~~:

avoid any contamination of the crystal by strongly boundJ Oxygen

which has been shown to affect -'he chem.istry of- some hvdrocarzz-nS

on platinum (9).

3. RESULTS

3.1 Cyanogen on Pt(ill)

When cyanogen was adsorbed2 on Pt~at 2^05 *< :on>.' 3.

crease in bDac'~ground was observ:ec_ L:n :h E a=rn pn

heating of the sample no orderi.ng was o'-servez.

Thermal desorption spectra (7--S: of CIN a4fszrbe-_d a: 25 K -,n

Pt(IlU) as a function of czeaeare sw nf: h

5

peak (Tmax - 368 K) desorbs a- a lower tem:erature from the (111)

face of Pt than has been seen from Pt(100) (- = 413 K (4)),• " " - ( max Y

Pt(1l0) (T m 468 K (2)) and Pt(s) (9 11)x(jl!)) (T = 405 KPt(i)(max max

(5)). The 8 peak (Tma = 780 K) at moderate to high coverages :s

very broad and shows no char3cteristic differentiation. into two

peaks (31 and 2 2 Even at low coverages, where typiay 32 Is

the predominent peak, only a single peak is seen. in comparison

to the peak temperatures for the S peaks on the other .t surfaces

studied the s peak in this exper:ment s most simlar to 3_.. On

the other hand 3 is t-p:=ay the ar er o- th = ' s w.S

3 on> showing up at very low csveraces r as a s....e to -he

3, peak at high coverages. No assi:-nment as to 8. or . is maje

in this study. 7his is consistent with the experimenzs of Hoff-

mann, et. al. which also do not cleanly resolve a -d 2

The ratio of integrated intensity in the a state to the 3 state

S approximately 0 .5 at saturation :ov_=-g-.

Our results are in good agreement with the peak temperature

for the a states as reported by Hoffmann, et.al. (12) However,

our observed a/S intensity ratio is very diferent from that

reported by these authors. 12 Quantitative measurements -f the

intensities in the work of reference 12 may have been hamnered bv

desorption from the crystal suspension, which they men-:on as an

experimental problem. Also the adsorptions of C2N 2 in thi. work

were done at a slightly lower temperat"_ re than the exper :ments Of

Hoffmann, et.al. 1 2 ) and this may cotiue:o t:-e enhanced ~/

ratio.

'97

N , % I.. k7 .* . .. ... , . -. -7 7. -. . . .. -

6

The carbon and ni- trogen coverages on the surface were fcl-

lowed with Auger electron spectroscopy. The AES spectr m o: a

saturation coverage layer at 285 K showed a C to Pt intensity

ratio (I at 272 to I at 237) of 00.44. The C -o N intensity

ratio (I to 272 to I at 381 corrected for the Pt n ensiv at

381) was 0.7.

3.2 C2N 2 Coadsorbed with H2

The coadsorption was per-ormed by first ad"zring, at 235 K,

10 Langmuir of H2 followed by the cyanogen exposure. Se:eral

experiments were also carried cut with - o csjo e a 4sorpCn

order. Aft r t he a- I ex p u0 e nu c _-E p r- s s e r .e-

nor was any observed during a slow hearing of -he sa-ple.

Several sets of typical TDS da-a :zr mass 52 are snown :n

ig. 2. As can be seen, a new C2 N2 peak appears wen cy-anogen is

coadsorbed with H2 This peak (Tx 433 K is verv shar=, c,

for low exposures of cvanogen, is the only. :eak coserved, " for mass

52. Saturation of this new peak occ,'rs a: approximat:ey 3.3 L

exposure. Fig. 3 shows the hydrogen descrpz'on spectra frcm a

clean (H2 only adsorbe-) and coadsorpt~on exc.rimen--5. .n com-

paring fig. 2 with fig. 3 it is seen -:!.: the H, itens:-v is

removed from the normal desorption sta-e an-_ shws u i.. n, new

state with Tma x 2 430 K, which is the same - Te a X

for the new cyanogen peak mentioned above. The shifting of -e

hydrogen intensity to the new state sa- -=se

o f c y a n o g e n ,, kih h c ,- -- s p o nds t o t h e s a t ,.; a - !cn. v t u=._ ' _ . " =.

2N2new C2 2 peak X). Uoon inoreasino e:s=ure :f yn gen _ne

a and 3 peaks are seen -ogr w in a :ianner Si-4-ar -m :ai -

d--','% W <" p * *,~ :* 4. r ?< 2 .. <. r < >Z.f° .x .. ;.>j- w - .. .. ---. - -- -- . . .. .. -

- . . . .. . . . . . . . . . . . . . . .. . . . . . . . . ;

% 7

clean Pt(l11). The major difference however, is that the ra::o

of peak area, a/S, is significantly larger in te case of the

coadsorptio than on the clean surface (Fig. 4). The ratio of

integrated intensity in the a peak (including the new 430 K

state) to the a peak is approximately 1.1 as opposed to the vaue

of 0.5 for adsorption on clean Pt(ll). This is not the case if

H2 is adsorbed after the C 2 2 * For postadsorbed H2 the a/3 ra-io

is 0.3, the same as in the absence of H,. A i:_r7 enhan-

of the a peak has been observed by Lambert, et. al. '61 in exper-

men:s on the coadsorption of C N2 -nd C o- ._ P "

exper::na w.hicn consisted of- an exocsure of r of CNha

L CO onlv the a peak is seen and tne 5 p.-ck is com '. ye elv 'i -

nated -rom the desorption spectra. 1t s.ou-1 be no te - at i a

our experiments the a peak is somewhat narrower in the aresence

of H2 (compare figures 1 and 2) . Lambert also coadscrbed 10 r

C2N 2 with 0.3 L H2 and recorded a significant amount of HCN

evolving from the surface of a Pt(!!01 crystal (6). No"2

spectrum was reported in that study. We also have noted small

amounts of HCN in the desorption spectra. However, a small HON

imourit in the cyanogen makes quan-ification of the .moun. of

HCN from hydrogenation of surface CN difficult in our expe:i-

ments. The substitution of D2 for H 2 n the coadsorption di4 no:

resolve this issue since DCN (mass 23) desor' bs at the same te_-

perature as CO (mass 29' which is present in small a-7onts fm-,

the background. The amount of HCN produced in our exer-.ments on

the Pt(lll) surface apoears zo be much smaller than the amzun:

observed by Lambert, et. a!. from the Pt!!', s~rface. The order

8

in which the H2 and CN were adsorbed on the surface mad no

effect on the generation of the 430 K state. in either order no

dismlacemen,: of the initial adsorbate was -detected in the rass

spectrometer during the exposure of the second component.

3.3 Ethylenediamine and Ethylene-d4-d amineA.

In order to investigate whether the new nea t S

spectrum of the cyanogen coadsorbed with H2 was possibly due to ahydrogenated cyanogen surface species, the cemis-r- of

diamine (NH2 -CH2-CH2-NH2) was also studied cn this sur-ce. .-he

onl.v products seen in theC -orm' desornt nsf "wig e: :zzs-res

at 290 K were H2 , HCN, and C2 N2 (see Fi:. 5).

The broad but well-defined nature of the :i, resortin=-s:e-

t:3 suggests the existence of two overia0oi_, 1 eaks pcss-:,}"

comin from the secuential dehvdrcaenation -z the am n-.

methylene groups. To resolve this question the e-yenjine

experiments were repeated using the se'ectivelv deutera-ed ethv-ene-d 4 -diamine (NH2 -CD The therma desor o .

for the H2, HD and D are shown in Fig. 6a. it can cdearlv be

seen zhat -he amine groups dehydrogenate at or ---st above tne

adsorption temperature and that the methy.yene" groups are -

genated at higher temperatures. The maximum in the rate of _e'-

drogenation of the methylene groups occurs at the same t:r-ature as the maximum in the- 420 K desorotion oeak of C2 s

phenomenon is discussed below. Fig. Ga also shows a sumai::on z:

the H HD 2 desorption spectra and this summation is ccm-

L. pared to t-'- H2 des-r-'on s-ectra f:rom un/euer- -v' _n-

diami-e. Te ac e nent s e...r ccd

.... . .... . . s .--

.4

9

4. DISCUSSION

4.1 C2N 2 on Pt(1l.1)The thermal desorption spectra of cyanocen from Pt (ll1) in

Fig. 1 show a good qualitative agreement with exoeriments z ,arredout with other Pt surFaces ((100), (10), and stepped 1_l1).

The low temoerature a peak exhib its no shift in peak -_ =-'__

over the exposure range of 0.1 to 10.0 L, which is indicaie or

a firs: order kine-ic desorption procesq. Using -w~rds rela-

tionsh ic between T the w idth of the descr p- zi oe s an. .. ..

activat:on energy of desorp-on (7 orrfrs- o desc'k +n e zi c ,_ _ he _ -c:riv a tjc n e n e r g y o f d ea r ro ri o n f o r h e a z e~ k ,

:ound o be 10.5 kcal'mole. As we expec-:, :-:s _s s::n t'; es

than t e value of 12.4 kcafomoe -.3e- ------------- 3-----a

of cyancgen from ?-:(100) (4). The fac: -ha: -he ae-.' s seen

to be first order on all the P sur:aces t-s f-r s : "

strongly supports the hyp thesis t-a the peak is -esor:-

tion of molecularly adsorbed cyanogen. A ccmfe=- s . -he

desorption kinetics of the a state on Pt(!i) which will allow an

independent measurement of the preexpcnentia. and actiaticn

energy is now underway in our laborator.

The 3 peak as shown in Fig. 1 exhibs a decrease 'n -he pea<

temperature from T 8 = 780 K at 0.1 L exposure -o =

at 1.0 L ex osure. Above 1.0 L the peak temperaz .;re seen to

increase to 1", = 815 K at a sa ,uration exocsure of l .0 L.

La bert's inter retation of t-he s tat e as rec n -:: nz fC '

groups would account for the aoarent secn - - na 3-re o: :ne

8 peak at low coveraqes. However, :h f 2 0. ", ;e a -- zr0 :.re

13 , ' .' .. ..,...- ........ ...- ' ' -'. ' ' .-. .-.., .. , , , ,. -- .-." " - "-- +' % - .., , - .. .. +, O'"'.e''Z +'' '' ".+.

V' _W --- .; _--. A.-' _ l. .

10

rises for exposures greater than 1.0 L precludes the assignm~e:~t

of this peak to simple secon~d order kinetics.

Based on T for the a peak of cyanogen desorpt-ion reportedmax4_j

in the literature combined with this work, the order Ofr activity

of Pt surfaces is given by:

Pt(111) < Pt(l00), Pt(stepPed) < Pt(l1O)

This same order correlates well with the relative areas under th'-e

* 3 peaks of cyanogen coprdto tea peak at sazurat:on. On

clean Pt(111) , the integrated intensity of the 3 peak I's ~5%

integrated intensity of the 3 peak at sa:uration. On ?t"10" and

P s tepped) the a s ta te con t-=Ins rouch*>1: 2 5% of :n eaed

intensity seen in the 3 peak. On P 121 C) t he a p)ea is a Im s t

no ne xi.s t ent wit-6h a n i nt e gr a ed int e n z i v o n I 5-10% of h

peaks. This trend can be seer to ext.end to two, more ac:ve,

r fist. transiticn series elements N,, (1!-!) (10) ,which leac-s t

complete dissociation resulting in N2 prodUCtion and Cu(l (

where it is seen that cyanogen desorbs exclusivelyfrmth

state anei the a state shows only weakly at very laeexposures.

On the other end of the spec tr um, cyanogen desorption froml

Agtll0) (2) shows only the 3 state. We feel --hat the- ralative

Insensitivizy of the a states to the str*ucture of the ?tsurface

favors the concept of a paracyanogen type structurefo th 3

state as proposed by Netzer. However, the recornb-'7at O n of C ON

groups Can not be ruled ou,.t without furthner spe:tr:zscopic

studies. 'Combining our results with previozs resu_"s in :~

* literatuJre leads us to the more comple-e rfe of ra:vt'0

the t ran siJ.t ion ne t al surfaces s t,;,4- sc d 5- t'war:3 -

<< ;;,_'< <3 )

4.2 H N ao

When 10.0 L of r. s c a s d. w cy a qen cn

-. -- _ ,a new state at 430 K, wh!:h we s.a esiz ae Ys Y, :

seen in - thermaI Ce:or . -o. s-pect n o: mass 5 2, , .:

low coveraces of cvarnoen the y peak s n -y o. p esen -reaches sa-ura-ion at . 3 L:' - c " Ao. . . .-Ks,_.3 cya. . -'ncce- _ . .-- cve a S ex cs .: r e -

d y - - = -* .C.

a k at 32 3 K to -he new oeak a t33 K. A I If 4 n S

seen t o desorb fom this hsae em .a:es : :n

exposures r:eate:r than 0.3 L. Th - ss :- ne Sa BC 9yan:- n , c S'

wn:ch corresponds :z := saurat:on of :he y peak In -he -ass 3

-- ectrum. The facc t t.. h I;d . -r n a nd :y an- en S c a--

Tame tam erat'ur and that satura: n -f t'-- i e-- Z: ; =- a'

Occ*-':rs at the same excsu:re a:f cyanc ind aytes -.... S.. 5a:

amount- o f c anocen 03 " i s nd -a a. : :. =: .n :: en-

... 5'" 2 - *" , .. - e -- e = .. = " '- " "

on t . u--a-------re e oeau aehe aU s

Point th e hydrogen and cyanogc en simu ane us / I y e--- . -0 f

the above resu.s ate i.de ,e -d_,_ of S-

:ion; H2 first ,or C2N

- .

The n.ew sza -es 4.~ 1.~:e 1a 2 :40*1 Ke::3 3b:oe

spec-:a (TFi. ~') s a :aXaC -3 45 n a -. *,

-eria:e a: sl. .*-:".: abov~e -- e asr:z.: '-

7hs*ed ds::on whiU' eaks at a S,-, I

a -a; :es::w: :

o N

*~ I w~: adso-,oe, :- ; : :: r. '. zsved n

dIC s. t cart be seen~ fr:om figu rq 5 :'a nsa:

at!: e c ncer.r: 9; n. a;e n is- s:s:::

'.2

Th e m a SS e ea'< - :ur . .4

.4, 2, Z'; a

n s- a a* z4. p s n a -

a *l Z V. *. n I

dn en" e nne 2. e c. :< -.-. .B ds-a ex e en-h-. :s-

dc:nir = - - '.ccen "rv s zr.- :.. a=:oear -2 .. -e -£ =5'

• .r -- . " : ,- - .~ h -: . : a r

surfnc ofen N i caso - r.

on ?:.00) by UPS. They cs:e a n'.ew in th u.S scec-

t ," wh* i '-.e_---,-z to "a-.-= i -e n ~ _ _ ~ z ".=- z m " z

A" = " ".'"-.. s :ra-e." .h ffi a..--- :- "-:s z_ ?.. - " '^-2

7- -'. - -_

z, an - ~ -* n

a tnch m icr-_ a i s o...' - e : . . s _ .a" I . .... h y I= " - ... n- e2 ' d w- z'- .-- -

p a otnte:-3s_:,nc: asect o4 c- c a:! c n

c-an > . .arz.. case -- e _::r :,r, :n -4e -

scr=-:ion axeriments this :a:io • s *l weres i: is e a i

*2-t'-e n Se -.

Sh U:~e ~ a do~~ 0 : S 'n 2. -a. S, f c

a s s. ina whic- o n>1 t he a s t a : was czi n ae.5

235 K and :e 3 sta- wa s, c -- 7 a

a n -.- -- .e

e: n e 3. :.a -

. -, .= ... .e.en -U

;' ~r r:_ : a"20r - m O . . ..= ,i' r .d .- . . C. .i S . V. a . . -- r

711

t'- sme i e o-e i -.- s -_ . exSame :ce .-t - : .:: -

d/3 a::-cl: by ~e c3:s o co-d-anma:ica2__ .> a.fec-ed bv. . -eadso':--" o we a-a e,- -o ":.e .-

.cusion :'-: :'e -"state is prese.i: -n :-e .-. c =_ : de

... n~ of 235 K as f . -- : sed r z :n_.

: ;. be -h .e /C a S,,a n n - . e. -

-" a cw -4 - .. .. --:e f s r- . p- s _ z-MSS

f 1 r 0 a .: c 3 7. -2 -re-nn -w - - 3 ex , we C .--c: ... . - -. -

-=-ow._. " i-c be av r h > e.,s_:._ a hc- ike_-ex. :f '!.i re--. - =-:.-.

W-rer r3) have shw= aci t'.e * e s- ~ o-.~ <ca.' -oeWh.- =- l _'= m e x o e -=

Oso ! < -^n . = S S' --:s ec : -ha" -' = r

e'i 0 's aeaanio:.n.

w k :a , av s---.,o;n n , cm. p = a s ---, o f

narrow desc:ption peaks =an be t-e .. .. 3" an -- u::! "o-a

orocess. Since the cyanocen f:m t-e dehyroen3::o. :-" -

e-1 ee -tr-na i s formed on th e a s a-ce aat t eer s S;e_ - -

t.h e cesorpton t err: _--a at.-B of m -3" a -'.- - e .e -: s. e

may be :he resu I o-f a se qen ta remoI;a of I a.

gens wi-h se;eral intered i_: sz.ies To a.r-s a - u aSS --

a more-_ ;t-i a. d 1, -ine :c s:utv iS cur iv b .:: e. .

this lab. These s-ud'es shc~l! shef; i :" :h - rzf:fhe

Unusua. kinetic beha_.izr of:e "tae"u= S. u a - 'e Y s-a--3.

The de.::cen. in --- ,ene nn e3: :_-:_ .3e

po dZ c " " on o: .-.c~es- -.n:':s : -h' "" e.. " . .. -=: s "? '

.- " . ." - *-' - .- '- " " " "

M .*. * * **

decc~osti e s~ C' e: e'.a - T h a.e is tz~ aa :

tiaily hydrogenated, species on :he cufe soI b e n c 7:

that 6tne d=ehydrogenatzn o : o zs'c:~~

ro:-nat--c-n o:f any of tl-e 3 sta:-einzn :-- anven, e s n e

an z - c :a n1 0 f t'-e me z-'c~ S:" z: o e e:~e-e:::a'

n e S' r*~ ZC Cc e -3 s n -_:g n

tihs i.:e s c h a~ at-'c.- l

~r~e~i::o ::the carzcns :in :s spec ies m.ay ::-an bez ::ere*

toobe un,-s u a s -n ce -3 e t' _c a s a a n o:A ~i -- c:> nea:

the sur-faca. ?ec en'z wo rk on rdeu~e au ex ch~anze -z: >f :e n

r,- pe ; , ?I I '

worker s'- and -;bach nav= eosr~~f~eH exhae

for this sopecies whc' also involl-.es hvranexzohance nj oz- l

a car'zon atom no-- bor.ded z:e>: the sufc. :Is Lnz=r-

es::ng to specuiate a: this po-nn; as -o cn~h: ns: h:a:

ac t 'i a zion of C-H bns fo:r -cn a toms w h i C~ nea a:~.

r em oved from th e s rfa c i ;s i n ed a g e nera.P ~hncme n a

Jhe :o a -1s or: on :e.sr nf an7 5,; an ah~~ : n

genat-.-. cf ate: and K e:'e :.?: 1'.

au~:a-e n-.-e: -e, - e.h;K-edi -- e ne .

0:- a v a t5 ad 97'.ze C- - -

w tn - - er, :-v .. i-. h_ -n

Sam oved at Zr t'ig" iv S g e e 2 r : 0r . -'F'D-3c:,r Z:dS. -

.._- n S -mc r $,o ..a B s -=:mn .-I S - h s s s =

underwav o d - -...a a d. 7- a

- = e3.._. a we.... as :he kin.e:i:-s 'hw ii=:: .. _ r s : -es r

z, _.. a: -3.0 K.

Resear .

4

... .. & , , , .M a. .- .:

. Cc noen {as mos 32' -herma. ;=czi. s=-a =

various exzCsurs af cvoc o n -r- ar r --

is -K./sec. The base 'nes f-av bee_ s-!.i f : .c:

cL ari tv.

2. CYanocen (as mass 352) t' -:ma sz r ' e: n 5 c- --

-;a-:ous cvance.- . expcs're " a - s Cre " -* ,°_

c s : oz sur:ace.

:csta-zsorption o-: var:cs e:.'-::sreszs- c.anccan,- ..

experime - l0 O.L expos_'r :- H as "-

zCro.;a:son of te cvanogen as mass 5- !er:

- fOm a lc=-an and hn;eroaen:-e a'-r-4 ?J.) sur--_

Thermal desoro:-:on soec--:r.a oo .; _xcS-.

et.Ile nediam .. -zo a C-_ -. s a C. :

mass 2; center is 4CN as mass 2; . .:3oZen as

mass 52.

2/-. 2 " _N*S.*H2 *. ,SO _CD2 _O -. H' - - . .. ~ f : _

2-C 2 -CH 2 d .L,2 -2. 2 2

2 2 2

2-2 2 D 2 2 -- 2- - 2

2- 2- 2 2 . =

.b (curve 1, a n HD 2D2) X .3 2r"_ _ Si..la -Co Cso0 red on :i,.

"2 2 2 "2

NA1 - ..-. D 2 - . .2 .. * - --- * ~ . . .

'T"? :,":*'; ':"? '," :" *.: "'"- *" "S-::-.:"-";:::;-<:

- r-

(2) M . 3rO*!C a R.A Ma ' :b w a .

57, (19-6) -413.

(3 M.E. 3r --"- and R.M. ame.:, - . -_ . -

(4) F.?. Me r, Surface Sc:. £, , ..... 2.(5: .?. Ne7:zer and R.A. ".74 ~ : Sc . 4,

S,1 '- --- -- - ---

' A .,e-. = h -, . i_ e r c .(9) v C - Br ,z .. 3i e.~.'m e - - -- = = .- - - .. . .

0 7 7) T r S.

Chem. Soc. 101-, (1979 5-.

7, " B = '. . . _ _ " ,.', .* =.- , . -.. .. . ... . • ;r "" a.'c R... _.. . , . ,-' z: r .:r -3 -" -- * " - 1

(1932), 456.

Copys .viol ot)I osr

( 0} J C Her~n!--= -= L "-: r- s a . -2 -. n c.-_ - =

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