Ionic collision processes in mixtures of methane with carbon dioxide and nitrous oxide

~.: ~ ) ; E l s e v i e r -

Sci~niific--Publisliint~:_Compan~;~.

A ~ n ~ s t e r d ~ m - ± - P r i ' n t e c l fii ~ifie N e ~ i ~ r l ~ i i a d s

?(-: :::),-

DIOXIBEAND NiTR6Us -:K~.R.-RYAN:A-2qD~2-W2-HAR~7::: :- Na~tionaiStandards

(Received

~.June1974)_

-~-ABSTRACT

_

:7-

gaboratory~Sydney

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2008_(Attstralia)

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: :-/"Ioniccollision pr0cosses.which oceur_inwea-klyionized.mixtures_ofmethane : Witli-nitrous~

oxide

~and

carbon

di0xide

~have-

been

studied-while--the-ibi~

are

"

.: contMfied inl~a -~(i30tentiai ~well ?generated byi_an ~eiectron? space: chai(ge.-Wilere comparison is possible the results are inreas0nable agreementWith: other recent measurements. In-addition, the .present study has allowed~an-b~sessment-of t h e ::rehitive -imp0aan-~e Of electron transfer mid hydrogen atomabstraction ProcesSes-w h e n ~ e i t h e r N z O + - o r : - C O ~ + r e a c t : w i t h methane: Within-the-experimenfal:error, -the combined r/~te-e0efficientTor hydrogen-at0m~bstraction andelectr0n transfer reactions with:methane is the same for~both-N20 + and COz÷~-.: However for N2 0 + 0nly One reactivecollisi0n:in i5resUlts in el~tr0n transfer, while:for C 0 z + ~:e~eetron-tran~fer occurs for 0he-reactive collision in iour. ~ -: - : - " - : =~--In mixtures- of nitrous oxide with!methane_ evidence:has-been obtained : f o r the~ product!on of..m]e,"30. Threshold measUrements--reveal-fhat both ~N~O + and OH.+ possible.precursor ions. I n th~ Same_ mixtures-it fias been _found that CH~ :~ will react with N20 but that= the~observed ~/ite coefficient rises from 0:to--0,53~ 10----9 cm 3 molecule- ~ sec~ I as~the i0nizifig electron energy_-is : iricreased=l'~om ?tiaethreshold-for-ci-/3-t-: production tO ~2OeV:~This observation is ~--t:aken~-as ev]deiice f 0 f a r~tction p/~thway which]nvoives-0nl3~iinternally excited

INTRODUCTION

-?= 5._ . . -

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"=: " _=~--~:-. " : . .

-

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:--.

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:: ~ " :

-:.~-~,-~::-,,-~In~mixtureg-of/methane: with-~'either-:carb6n? clibxide; ~r/-nitr6us::6Jdde] ~the .

i

-in the -energy’of the reactant-ion: It is~We%hnown that~some .~ ionic reAction -r&es ,. are-influenced by both~the~internaland translatiomkenergy of the &a&int~species [6]. Since, mgeneral, the available~expei-imentalmethods-do not alloiv~~&e~uniqtie .: specificatio&f the-eirergy.st& bf the io&~‘differences inme+urred r&e coefficients ,. -mare:.tobe expected- Sc&e &the ~difficulties&&c&ted with the evalu_ati& of the relative i~rn&kmce~~‘of~these’~t&ojsources of: discrepancy are .discussed. further’~ .b&& with-referenceto some rectkt ir&&rements of simple reactions in methane; _~. of :methane and-. carbon :dioxide are_--about‘ _ 1 Be&use the proton all&ties’ ~v equ&[4], it is found that-when the equilibrium _. .. -. ‘.. .,, -. ~~’ .~-CJ$+-+C_H+

+~C&;&j~~:

.~ -_

-_ ‘:

w

:

is ~re&hed, measurable- qu&ities of both IC02H’ and CHi+- coexist. This has ” allowed the measurement ofthe;kquilibrium coefficient K,.by Kasper and Franklin ill, &ng.high-p ressure ’ m& spectrometry, byBohmeet_al.~ [3] and by Hemsworth ’ et al_-’[4] using~lao$ng afterglow methods ~and,“&ore recently; by, Harrison and Bltiir [5] using the trapp6.d ion tckrnique~.The Jarge discrepanciks’observed in the;value obtained for K;.have- been ~attributedto the fact that~neither-the method of _ Kasper~~and,Fr&klin -nor that:& Harrison. at&Blair allows the ions to-at&n _t&&l

equfiibrius_

I~

= _ ~: ~. _.

-_..

-I

~. -~_.-

-_1 -_ .- ’

Presented~belo~w~ are the results for rate coekcient &easurements for several reactions .in.lpure methane,- iii -methane -.. and- carbon dioxide mixture& and- in methane: ai+ nitrous driide..~=~~res.:~~ese ~metisu&k&& have &~b&~~made-’ -u,&ng the ionltra~pi.ng .technique and by ~cc&rolling ~the!p&ameter~~~so~ that -the.‘~’ I.-&an translational- energy of-thel prim&y ‘ions is kept to- LO.1 ~eV~lThis~point is .discuS~Sed_fu;ther.in:t~~~Expeiim~~tal&ctio& r’ -: :. ‘-;m:.I.-_e ,: ;_- -...... ‘_~f;~ ‘: _ I_ I ,.;I .- ; .::

,

~_~..

1 _:‘= j

r-

-=I /

-_:_y,-_

~_. : _~. ,-- .~ ._ -r,--‘_-;-._, - ;-

-_. .;‘-m ~.I<._ _ I . -_

_- .~:-

C~

_~; -.-~

_-

.. ._.

0-I 0

-_ :.

~. ‘..:

mod -- 1mo.3000. REPELLER PULSE

I

I AODD

DELAV

.~

-. 5000

(/umcl.

J ‘000

-.~

:.

:

-

_.~

- F&i. Trappin&har&te&tics obt&ed for Ar+ in pure argon. The well depth is &ected to-be’ prop&o&d to the .gap curient and the calculated depths are shown orithe figure_ T-~. ’ .~~. 7 i _

~d&k&d .by-kyaii -and Graham [9]_ No changes have b&i -made ekher_io the a@p&&or in~tlie kqnditions em$loyed in’~thatstudy_ Calclilati&ind~cate thatthe&& gha& well is less ihan 6.1 V in depth &d-the resul&‘for~&TAn puk &go& shdwti’in Fig. ‘1..suppok this. The well :depth, v(rliichis-e&petit& to be propbrtional,to &&&-curre&. [COJ,iS seen to be too shallow to trap k&y.&when th&~cu&&is 2 ~~mp,‘but~.when- this .is increased to 4 _JIZI~~~ &.&e gd -t?ap@ng

::200:,

::: :x

i: i

m a d 6 a Compilation of values-for thiS:reaction coe~cient~(Tabie:IV. 1/el.-.[6]) ~a n d : c b n c l u d e s t h a t it is 1:2 X 1 0 - 9 cm3-molecule-r ~ :see ~ 1 -with_an~Uncertainfy~of,-~ . i x 10-:30 -cm 3 molecule- 1- Sec- 1 ~-Thus the-measurement-made, here ]s_in~ close: :~ " agreement with _values :obtainedbyother.-ineth0ds[;--:=/ ..... -:7 - . ~ .>; ~.?.=<->-:i~: ?.... i._7. :~Measufemenis:sh0w:that-the gas flow is-m01ecular andthis is~SuPported bY t h e r ~ u l t s of-R. yan and~Gi~aham ) [9]. wn~6h Showthat :a- f0uri'olff:increas6 in(the ( -reserv0ir:.pressure:had no-significant effecl~0h the rate coe~cien-ts 0biaineff t'or :t-he reaction o f e l l , _+-.ffitli methane Or H:z ~ :with h y d r o g e n . For gasmixtures t h ~ I s u m o f _ t h e % comp0Sition-f0r-eac h c o m p o n e n t has :been (i00~l)~/o~in aH :cases,~ - While/the_. -. error..inthe_ .--~c°mpbsiti0n-ofanycompon6nt?iS_ _ _. . .=< 1 o~ of Rs value.:_/- - : ! -:has

-

R E S U L T S - A N D D I S C U S S I O N

:

Reactions in pur methane

-/

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-

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Bei'ore i h e :resuiiz o b i a i n e d - f o r mixtures of methane with nitrous ~oxide Or~ : :carb0n~ dioxide can-be inte~reted, allowance must be m a d e , f o r t h o s e reactions which occur in:pure methane. W e have measured the rate coefficients for reactions of b0thCH4 + and CH3 -+and obs6rvations of the secondary ions produced'indiefite :~that, under:the preVailing-conditions, the only. reactions which occurare- ? -- -. - '-

:-CH4++CH4=4 CHs++CHa- CH3~-+cH"-4

C2H54-+H-'2

-

'

-- -"

-'-

"

-:- -

- [ ._:::: -(2): -

"

-(3):

- Measurement-:. of_--- the --:-rate. -' coefficients .- for- --these .: tw0---~reaetions yield. ':(i-22+--:0-02)x10-9 :~cm3--:(~olecule.-!-~ sec-~l. : and-_ ~(!:.3i:q:0.04) x 1 0 - 9 . c m 3 _:molecule- {: s e e - '---f0r teacfi0ns-# (2) -and. (3) -respectively.. A s pointed -OUt in' the : Experimentat: section,; reaction-(2)=is u s e d . to ~ibrate_ithe~fl6w system ~and~ali :other tatd-eoeffieients:afe~-refdrred~t6 it_-~:: _:. - / - : , - : : . --~:::~-~-;/~--:'i:--:::?--<-~i ~-- .:,~--

:~:~,'7~: :Table 1.illustriites~.thedifficuityl in assessing-the reiiar~i~ 6f-rate coemcient ~! meas~ui-ements~even for. th6_rdbaively_uncompli~ated~xeacti6ns:in/xfiethan&::All of:, (_thb~measurements- rei~6rtedthere lmve b e e n m a d e : b y 0bser~in~-.the a~tenuation~of,; ~-~_ p r % a .ry.i o n Paflaer: thah. t he~ p ~ d_~cti?0n~of the:~=C-b n d a r Y i b n : : F ~ e r m 0 r e ; ~ i t h ~ ~ h ~ - 6 x ~ p t i0n-6f Her0-d~ailtl~:Hari-ispn~[8 ]i@:auth6fS claim ihat-iheiri-measurefiJen~ ~

,3~m-9_.re:~(~fehe~ve? i{6-m~pilati6n~-iff-~iV~ff~-b3¢>H untli~s£~nff- P i n i ~ 6 t t 6 [1B ]),)a0es: ;

:~:.-~:~: ~: ~ :-.-~:-:::'."::: :=::-:i::..:": _~ :~- _:.i,::~ ! ::i~- ~-~ - ":-.--:~- ~-?:_ ::--- -~i".--:--:~V!:::-.,i-i~-~-20i.--:~i::--:-: :~

Oi~.-RECE~

COMvm~Ti0~

::-: :-.-.~--:: '.:? -:-: --_.

V:~LU~

J"-' ~:~-'Flu~#-~e U 2 ] - - : - H e r o a a n d - \ - - ~

--

--CI-I~+--+CH; .-~:CH,+=~-CH~

- CH3+q-CH4-~

`-- /I.2=

:--

':i.20 :

c : ~ H s + - t = H ~ --'- . 1=3-I-0.1 - :

Reaction:rate coefficient r a t i o i~:-

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& C ~ , + / I ~ [ - ~ , * : -

-

~

-~-

1.154-0.05:_

-

:

:---.:-

a.capacitance manometer pressure measurements.

.-i

--

--

[13] :: ;. :ZluniFe_ss

?FutreIl

::--•I.20::

-

1.30

=

~- .- i.11~" 0.04""

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::1222 :-::::-:-:?::

0.89+0:03""_-:

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:- : "

-:

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reaction

-

1-3!-:-0.04 f =

' : 0.92 'J0.05 \ - - d,25--I-0.05

attached directly to:the - " --- - -

.

ahd.:-i: This W o r k ~

- -

" ~.

- .- .~ .-'- 0.92--0.07- ? :: 1_04~0_05

: a Pressure measured'using -table 0btainedusingindirect

-:. :

CH,~'_ -A~.o. C~=~-+.DEC.~Y~_ V m ~ E - - U ~ _ n ~ , ~ ~ . :::-.:=

y O R THE_ m - n ~ C O - E ~ / ~ . 6 F

~

:-

"-- -

. - 0.93-~-'0.04 -

region; other values in_

._

.

:

-

_

" . . T h e r e - i z a m p l e e v i d e n c e [6] t o s h o w t h a t tlae rare cx, e m e i e n t f o r t h e r e a e t i o n - -• - " -of C H # + d o e s n o t v a r y w i t h i n H a 6 r a n g e o f c o n d i t i o n s = r e p r e s e n t e d b y t h e m e a s u r e - -_ " - m e n t s i n . T a b l e . I V - o f [6]. I f - kcn~+- d o e s :not _vary b u t there-is a real v a r i a t i o n_in -= -~:- k c m + l k a ~ ~ - , i then"kc,3+--- m u s t - - v a r y a c c o r d i n g t o t h e e x p e r i m e n t a l - c o n d i t i o n s _ :.~ e m p l o y e d _ . _ - --~i " ' " : .... : :-- " : . . . . . - - " : . -~::Factgr s w h i c h - m a y affect t h e r a t e o f r e a c t i o n o f - C H a + a r e t h e i n t e r n a l a n d . '_. t r a n s l a t i o n a l - e n e r g y of:the ion. I n o r d e r tO d e t e r m i n e t h e effect o f excess i n t e r n a l : . . . . eiiergy o n k ~ , , + weilaave s t u d i e d r e a c t i 0 n ( 3 ) as a f u n c t i 0 n o f the electron energy " -; - - n e a r tile t h r e s h o l d f o r - C H 3 +. 0 u r - r e s u l t s , s h o w n i n T a b l e 2 , m a k e it d e a r t h a t - . . Y=_~!-: t h e e n e l g y o f t h e e l e c t r o n s u s e d tO prOdUce t h e C H 3 -+ i o n h a s n o m e a s u r a b l e effect, ---:-- i i i - o u r : a p p a r a t u s , o n :the s u b s e q u e n t - r a t e o f - r e a c t i o n Of tfiai~ i o n . T a b l e 2 - s h o w s \ . _:!:~ = i--.-:-:----that 6xa~t~y.ine s a m e : c o n c l u s i o n s m a y b e - d ~ a w h for the C r ~ _+--ion_ Whether the :::---variation o b s e r v e d : i n T a b l e - 1 for-kcn,-~/kc~3+ :is ca.used by. t h e U n d o u b t e d _ --: ! ~ : : . i : .diffefeficesfini~i0n~:velocity d i s t r i b u t i o n S o r - b y . - u n k n o w n insti-umental effects is . . . . ::~:?: .: Uncertaia.:H6wever, it Seems l i k e l y - t h a t s o m e i n s t r u m e n t a l " effect has-ii-0t: b e e n - ~ .--7%~ : :-_:~:, ? ? _ t a k e n : i n t o - a e c o h n t i n t h e : w o r k - o f Huntress- a n d P i n i z z o t t o . . : - .-? ~- :-- i : : -fS ,

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&e&i&s

iA mixtures ojmethane

&tit n&-ohs oxide

1

.

; ~_

-. ‘It--is

doknated-by

to

be exp&ed.. that: the ionic- chemist&- Gf. these- &ixtures- will be -: ’ 1 reactions (T), (41, (5) and (6)_ _I -- .~. .

_~

CH4+-tCH4

-, CH,‘+CH,

PI-

CH,*

+N,o

-+ ~;oH+

.(4)

N,O+

+CH4

-+ N,&H’+CH,

-.CH,+fNzO

+CH, -’

.=

(3

-~ ‘- -.f6).

--+ N;OH++CCI-Z,

Ion cyclotron resonance; ICR, studies have made it clear that .bdth CH4+ and.._NiOf react rapidly [2] .and, m additions to reactions (2) to (6), the much siotiey reactions CH,’

t-N,0

4 NOH+

+ CH,N

(7)

and N,O++Cti,

+ NOH++CH,N-

(8)

have been proposed_ ~. Typica! results from the present study are shown in Figs. 2 to 5. For NiO+

the removal rate is uncornplicatkd.by opposing reactions and the ion intensity .is seen to decay in a siniple exponential manner yielding. a rate .&efficient of (1._17_tO.O7)x lo-’ cm3 niolecule-‘.sec-’ which is in satisfactory agreement with a combinkd coefficient of (O-98) ~~10~’ cm” moleculeWi sect’ found by McAllister [2] for ,reactions ‘(5) a&(8)Examination -of Curve (A) Fig. 3 reveals tha’t for ,. I

I,

I,

1J

.~ _.’

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mm: -.~ ;

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PULSE

R E P E L L E R

1000

D E L A Y

I~00

2000

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(/,¢xoc)

Fig. 3. C H 4 + d e c a y c u r v e s i n N 2 0 / C H a mix'tures. C u r v e ( A ) o b t a i n e d f r o m ',-o1~1 m i x t u r e ; t h e s t r a i g h t l i n e r e p r e s e n t s a least s q u a r e s fit o u t t o 7 0 0 / / s e e d e l a y . C u r v e (B) o b t a i n e d f r o m - - - - 4 : 1 N z O : C H 4 m i x t u r e . T h e s m o o t h c u r v e t h r o u g h t h e p o i n t s r e p r e s e n t s a fit a c c o r d i n g t o e q n . (10) (see text). I o n i z i n g e l e c t r o n e n e r g y 2 0 e V ; c o l l i s i o n c h a m b e r d e n s i t y 3.4 × 101~ m o l e c u l e s c m - 3 .

CH~ +

•

m/o30

•

N20 +

>.

•

•

o

-

•

•

~_

o

J.-

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•

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UNCORRECTED

ELECTRON

I

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ENERGY

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1/-

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11~

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.:_

-

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=

--.

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- \ - F i g . 4 . I 0 n i z a t i o n i~fficieucy c u r v e s ? f 0 r C H 4 + ~ - N e O ÷ : : m d ' - m / e ~ 3 0 _ f r o m t : I m i x t u r e 0 f N 2 0 w i t h -.: C H # - - C 0 l l i s i o h C h a m b e r d e n s i t y 3.4 × 10 i z m o l e c u l e s i:m-:~. ~:- ~ .- .: 2 - - " - -: ! .-

ina-1-1 mix there:is a Slight bufbignifi6antfdviati0n* fr0m-~ilsimpie exp0nent!al dee•.3k:TO~mp~[~e this deviation a ]6ast~sqfi:mr.es~plo_th@:l~en2dydWn~tl~6ugh~ :-,thelpoifi.ts fo~ .~egcti-onLtimesito700 psec-!t::can b.e/seeD:t~.dHO_:t~((th. ~:val,_fu~sf er::: ~:?~Hi +i7c~un~ts;at)T~actiOn ~-.times greate r :~than::700:/isec !"m-~iSysiei~/~fi~ yl)~hj~er-: CH~ +

....

.

-=.~

~_:.7.S,,27~.~.:5:/.~.~--~_."

:9.:-

'L-~:? L ' : -

}~--~-

-":-

-

-

~<2

:.5

,:-

-'-'---

"-

, ‘_.

Fig. 5. CH3; &&y curvesin -111 mixtureofNIO chamber densit&3.4~

withCHq. Electron energy as shown; colli$on

1012 moiecuJes_&m-3.

1

trader phenomena [yl. ,&I this partjcular~case the observations can_ be &lai@ if the reaction -- ‘h,O’+CH,

3 CH,+

+N,O

._

PI

occurs--Support for this interpretation is given by the,results in Curve (B) Fig. 3 -- which have been obtained in A-4:1 mixture of nitrous oxide and methane. In this mhure the reiatibe importance of the charge transfer reaction is increased, thereby causing~a.complete departure from a simple ekponential-behaviour f&the CH,+ decay-curve. -~ If-reactions (4), (7) and (9) aII’occur, ’ the e&ected dependence of CH,+ on &e is ‘gii&. by

= ~ ::

~::

~

= 3~/~:

~i -~ k/:~:~L ~

~:~ ~:~i~i::~i~ i ~ : ; ~ L ~ o 5 :

by:these Curve:fitting proc.edures. :Thus the:direef/measurementof~(k~ ~ks4skg)

:/results/in/a:valu6-of/(i =1-7+ 0:07) x lo=9 cm~ :moledule-~ -sec-_i.: w h e r e . ? 6urve : fitting proceduresyields a v a l u e Of (i:84:0:9) ×-10-9cmZ: m°ieeule:--i' sec-)~-ii: ~= :

: ) ~Figure 2shows a typica!result (or CHs + which is produced :t,Yr~ction:(2) and .removed b y reactive Collisions with : N z 0 - F o r repeller ~i:lelay=)fi~es:greater t h a n 700/~seo, production Of CHsq:. cab n o : l o n g e r be detected and~the-intefisity : o f this ion then decaysexponentia!ly. A least squares fit to: this exponentialdec~3/: : yields a raie eoemeient o f (0.79 + 0. ~0) × m--9 Cm 3 molecule--r sec-X a n d inb~ure= m e n t = o f the secondary ion intensities shows that=CH5 + / i s remOVed almost:; exclusively b y reaction (6). ~_ > ,: :. ? - - " The productio n o f a secondary i o n with amass-to-charge ratio 0 f 3 i has been observed in this study. This:is p r o b a b l y N O H ÷ which h a s b e e n - r e p o r t e d in the I C R ~studies 0LMcAllister. U s i n g double reso;,ance method~ he eoriclUded that both reactions i(7) a n d (8) occur a n d do so with the s a m e r a t e C0effici6nt-of 3 . 0 x i 0 7 ! ~ -em 3; m01ecule- ~ see 7~. In principle it iffpossible tO estlmate--the Contributions o f b 0 t h CH4 ÷ a n d N~O +- tO t h e p r 0 d u c t i o n o f N o H ~ - : i n . our experiments but its low intensity makes this impractical. However i t is p0ssible to get upper limits for the rate coefficients of reactions (7) a n d (8). I f it-is first assumed that reactio n (7) i s the-only process leading to t h e p r 0 d u c t i o n o f N O H +, then it can be shown readily that -: :

: [NOH]~ k9

k7 [N20] +

[CH*+ ] ° + k5 +k-IN209 ]o

(kT+ka)[N20]-t-k2[CH4] ~

(11)

where the subscripts outside the concentration brackets refer-t0 reaction time a n d the subscripts on the rate coefficients refer to the appropriate reaction: This treatm e n t leads t 0 a n upper limit o f ( ~ 2 . 0 ) x l0 - ~ cm a molecule7 ~-sec -1 for reaction (7), Which agrees within experimental error with the value 9 f (3-1- ! . 5 ) x 1 0 - ' ~ cm 3 molecule = ~ sec= ~ reported by McAIlister. . . . . . : ; ~It- it is n0w, assumed t h a t reaction (8) is the s o l e means o f p r o d u c t i o n o f NOH+; one obtains an upper limit of --~6× i 0 - x Z cm 3 molecule -~ s e e - x, in_p0or agreement: with ~the ~value o f =(3 + i.5) x: 10= ~~ cm ~ molecule ~ 1 se0- ~ f o u n d b y MeAllister. .;-~ -: ~ ... : : . y: :--:-: ~ThiS-study?has also?J-evealed the p r o d u c t i o n o f a Secondary ion ~Vith a-masst0Lcharge r a t i o of 30_ A f t e r a l l 0 w i n g f o r c o n t r i b u t i 0 n s f r o m 1 3 c ! 2 c H s + ( a h d f r 0 m " N O +, mass 30 aceoiints f0r ,L 2 ~ ,bf all ~ c o n d a r y : ion:prodUction.:Attempts tO: u s e thresholdmd~sueements t o establish; thei:idenfi-ty 0f~th~e ~primafy.ion :-whicla~; ! le-ads ~o i n ~ s i ~ o : : ~ y e ibeen nn~uccessfulf.~--In)?FJg~ ~4~ar~ :showmerude 39nizat!on :

; ~Pr-ec)s!on~0_f:the~eX~,-r!m.ent d 0 e s n o tfall0~ :eitlier~f=theSe~:ibns~to~be~bxd~_ddd:tas~:i

: )-i , a : p g s s i b l ~- p r e c u r s o r ,

and all ihat can-be stud js thai: at ldast-0ne0f

m e r e _ ~-Pr0bhbJ3)!i-:

::' responsible:f0r the pr0ductionof mass 30.:::Furfl/ermoie it is-n0tp0sSible -to-i_be ;7!

ofihe comp6 ii!o" of this seeondaryion-but:we note that it naay -: : NiO+q-CH4-~-CH.N++NO -- 5aft d - : . : - : . - - - ~ - - . : . . . . __: ~

-" -5

+

"

- -_

-

_

cnaN ! -:

-_~:: :)7.f~(12):~ _. . . . . . -

.-

4

_-

'~ "~e ex6thermie. " " : "_-. ,_ _ Shownin Fig.5 are decay curVeS Obtained f0r t.h6CHg +::!0n inal.:l mixture:: of e l l , with N20 for ionizing electron -energies;of 20; 15 and !4.e.V.-lt~can be geen-: -that the slope o f these sets of results-depends upo n the energy of thei0nizfng electron. . . This . increase . in slope-with incre~ing: electron energy may-be ~causdd: by : reacti0ns-.0f-internally-excited-CH 3 -~:ions- Because~ we )haveIShown, in:Table' 2, - that the ..rate:coefficient£orihe CHg + reactioninPure methanecis independent of: electron e n e r g y , w e interpret, the results: in Fig. '-5 as evidence for~a reaction- of :: excited CH3 -+ ions with N 0. Vroma consideration of reactions whiot W0uidbe : endothermie:for

the ground

state i0nOne

or more

of the following

ions

may:be

suggested as .possible reaction products i CHNz + (m/e 41), CHaNz -+ (m[e:43),. C H I N O +- and NzOH + ~(m]e45). Theabsence of ion signals, fo r m]e 41 and m]e 43-] :excludes-these ions a s reaction:pr0ducts and the masking-of role 4 5 by N2 OH:-. formed from re:actions (4), ( 5 ) and (6) precludes-conclusion s i-egarding the last . two runs. An additional~possibility is that exothermic reaction-channels for the- -~ -- . gr0undstate ionmaybe-suppressed by insUrmountabi6aotivafio n energy, barriers. ' Consideration of these,:and the opening of: such channels to the inte -rna!!y excited - - C H ~ + ions,-:si/ggests:.NzH + (role 2 9 ) a n f f iCH-aO+:(m/e 31)as-further:P0ssible i--. reaction produets.-However, as i n t h e Case of nile 45-above, the N z H + - i o n w o u ! d : : • be maSked by the C~Hs+ ionKormed by reaction (3):and;'tlle?CHaO ÷ ion is-excluded because-the low ion signal detected at:m[e 31,_andattributed t o N O H +-:

RF.AC~ON RaTE COErr~CtENIS'(Cm

:3

molecules

1

see-- 1 × 10 9 ) ro-.ur~ rdg~T~-SE~C-fi0N! - } ~,

- i ~ :~-~

Uncorrected electron energy (e~)" ~--Reaction raie eoefjqeienti: ; :)~ -- ;~"~ : :!.< i ~=::_--,.-.-i ~---/.: :~7: ~---

~

2-

2

2

£.

.-

~_

2

~ -

--

L

-~

2'-

:-"

"-- .a-{Vhldes:6~mp u t6d~Ugiiig lthe~mbJtS'tired ~alt/e-~f:_l;31~5<~l 0 ~ -9~/}.rh ? m o l e ~ u l / / : ~ : ~ - ! - f o C r e A ~ 0 h

"

-

Q

O)g{£~-~::

The e~lkrirnental results bf the present study are gummaiized in -Figs. 6 to 8. It is elcar from_ Fig. -6 that kO3’ decays”& a sirr@le~exponenti~l~r&ki-kr &rd’the .value dbtained for the rate coefficient, (i~i~~f-0.1) x lo:? cms‘~~leculc-~ set-lI_;: -_ -. Li

set is in good a&&ent with &-value of (1.07&0.09) x lo.-?-. cm? ni$ecule -obtained.by~~I%rrison and Blair 151. There.seemslikle doubt. that anerror in_the c estimate of :the .‘ion source residence timi: is reiponsi:ble f&~~the high _value of -2.3~k~lQt9 cm3~molccme” set-l rep&d: by KaSper-ana-~~~~a~~inl[i I_. ~. ; T Some-r&u& for dHk+ ~retiosal are’ shown :iti.Fig: 7; HG-ris& and Blair &i&i &&t&j that:&: r&e of.CH,‘~ d&$&~siron~y eon the ,_ of.d&&e&ance~ I~~ionizingelectronenergy and they have attributed_thisto thcchar&tra&fer proc&s

--:-.‘-_:_

.~ __

_

- -

" I D O 0

~

. --.

-

+

+I/++ + o

+

+u~"O

O_

-"

++

-

o-_+o-o: , "

(+~---

.-+

_

+ •

-.

+

:~-

O+ . 0 . o

....

_"

+

• +

:-

-.

e+.,+.

"+"-4) --I -I

:-

--

_

_

+ .-

J. .- .:"

5 +-

+ -

--

: : + .'COzH~

-_+

I

._:

+

1 0

"

o

o o o

-

2 o o D

- REPELLER

~ o o o

I ~ D o

.

s o l o

PULSE+DELAy

(/~sl+')

-

L.

-

+:

+.

-

_

Fig. ~6. Typical i:haracteristics obtained for_ C H a + , COz +, C H s ÷, C z H 5 +. and C O z H +_ Obtained i n , - ~ l : l mixture o f C O i with CH.~*. Ionizing electron energy-16 eV; coilisiori c h a m b e r density . 1.7 X 10 ~z molecules cm -~. " " " -

•

.

[% -

.... O

.~

.

-

1.-:

•

.z

' 1 0

"

-+

+

+.'

."

"!/i -

,_ :_..:/:.:y-;--

J-

.J..~'+':~-'LREPELLER

S~.~:~-:

+

.

+

, -

/

_

+

+

" ~.

~--

-::: -_2"

+

+;-Z -~

-

-

-'-a

++-',"

:PULSE:D~LAY

~:++. :,-z+-: ~-++:

+-.+FJ+-.:7-; + C ~ d ~ ~

:

+

+---__+ -..!

~-+

" (~ilc)

":~:.'-.-':~+:-<++a

-.-~'.<;':.~ _'-;+::-:.'+ - - : : - ~.c ~ " ~

- ' 2 " - 2 - ~: : - - C ; " - ~

. •

<+

-

.+~-+-'-'~+-~-':+'---';:-:'~+--

.

+ ~

J-:/::-;++.---+*---- ":-- +:.t~

. . . . :.;-

~ :..

-...'~qr~ + + ~i::C_O_-~;[CH~(++C-2~t~+~(A). ~obt_m.'n-cd+: fr-om '_:N_1: I ~.~+.i_~_e+:of+:. c ~ . ~ (B):\:.~.

:-.~ 2 ~ . + ~ .oa_N -'aJ.i~g.-o-~j +:(:| 0)_--_] 0_-~ n g "ele~o+'+~i2.0 ~.'V;¢ollisi+~: ~ha 'm_bci":d~itY~ 3._:4++:] 0 ++ ::~: +'+~IML'4.JlC;:r~UlIr;;~

,I~LIUL

~+~. ~++,:~;

">~ . .

z + ~

+..

±,

~.

. + " :, ' ~

+

I

_(

_=_~ .-.

Fig. 8: CHjf -decay- chaiackkistic -from -1 :i- m&u& of ,C& with- CH,j: elektron etieqy 13 qV; colkioti chamber density 3.4 x 1Q’2 mole&k ~&I-.“.

_ a -111mix&c -mann& A typical i&ult for CH,+ demy~-In energy is showq In &rGe~ (A)

.Nomin&

-’

j

ionizing,

_

.’

at 2@~eVioti@ing electroti

Fig. 7. Two points are-in-khediately~ohiotis.~ ..

First,

thk dcpe&Ien_ceof C’&14’ on t&e-does not follow a ~im&expdnential behaviotir ;over.the 200-fold reduction of i&z&y shown. Secondly, over. de first order o magnittide_6f reduction df CH++, no departure froth a sitipkex~~onential behaviour chinbe detected... Curve (B)- Fig; 7 shows results obtai&d in ti-4:l do&H,-rkixtqre &hick h& been chosen_ to accetituz& thk~eEe& bf the char& transfer reaction on the

etry -11J, fIowing after&iv [3 -and 41, and-trapped ~ion&ieth&i$ ]$]_~:-A!1 _cf t.he.se investigations heave--shci$ that the. proton-~ atE&s of.- methane:; arid ~~carbori ~. 1d&tide are ahnosttequal. and; for. this _reas&a &hdystate~ c&--be :obt&ed~iu’ .: .-‘which. &&able quantities of both ionic species are p&e& The:f&ing after~&ti_ method~aliotis the,jon to. attain the&odynar& equrhbrium a_ndthis permits --. -.~’ an a_eeurate~measurement of K,,_ the equ~hbrit&coefficient,for~ CO,H+

-(_CH,: r

C&‘++CO,_m

:-,:1: -. _-~

-~;-; ..:_ ~=-_-:

_. -_--

-- pj

~ecent~~flowmg aftergiow~ studies have ‘shotin that,IZi depends-strcngly on temi ~: ~-eI y.-_ _. -. -1-.~i~ :p&ature within & r&&of 196X to 533 K: [4]_ I Although a steady .state -can be .reached in both the trapp,odiqn &d high. ‘pressure mass spectrometric $udies, au &zcmate measurement of &-is&t pessibje by these nrethcds. This is because the internal and transhttional euergy carried by &e ~CO*H’ and..CH,~?ibns will affect the& relative iutenSities~when_the steady. state is. attained.. A comparison ef the a&a&t vahtes of kYr,se obtained with values from: the fjovving:afterglow rnkj lead to quaht&e information-about ‘the -: Ed.- --._ dej&ure’from theftio;dyDamic eqnihb&& .~. Typical resuhs’for CO,H$.and~CHS+ obtained in our apparatus are sho$vnin Fig.:6. We~obtain a value of (9_;5’&1) for Kp at 340% which is to be’compared with 7.4 measured by Kasper-and Franklin and N 20. derived -from flowing afterglow meakrements. -Harrison. and Blair, working &t 373. K, obtained a-value of k8 compared with-a- value of A 16 -derived from-flowing afterglqw meazkrements--. . ,._ at the same temp&rature.- ~. Some comments -on- the quahtkive effects of. departure from Maxkell-~oltz&anir energy d&b&on are possible; Under suitable conditiohs of pressure aud- compositkk, all primary ions are removed. rapidly- and -the-dependence of _- _ ._ ,. CC$Ht and~Cj?lg’ on time -is then-described by

.

which-has the solution

-_

.are likely.to have a greater effect on-the rate coefficient for the endothermic-reaction (18) than 0.n-the’rate coefficient of the-reverse reaction. : ] -. _: ~-. ~1.: _ -..-%‘he re$u+ jnTab!e b-make it.dif&uit to decide if_this is true:- Certh~nly the values.obtained for k,, byBohme et al.; ~by @a&on and Blair; and by us are in : -re&onable &ee&ent.~z On’ the- other hand- the’_value of- Kasper and :Fra&hn is lo&r by-about &a&r of 5; Unless-this v&re may be di&mted~ it is not~possible to say that k17 is-unaffected-by the energy&f the ions. _However,.in comparmg our measuremen+ y&h those of Harrison and Blair we feel that-some conclusions may be drawn.. The experimental procedur&- used are similar and this suggests that the internal energy of the ions will:not ~vary$$ificantly bethen~botk<& of e&r& menti_ Accordingly the significant differknce_.in thevalue of k,, between e work .~ and that of ,HarrisGn .and -l3jair is probably ,ielated-~to .differences in. the me& ,Harrison and Blair saint out that-the raie transfational energy of -the-CH,+ ran_ of .the. :reaction (18) would be expected to ~&x&se ,with increaSing -. endot&&& energy of the CHj”ion. J_fthis jntereretation~-is correct. then we conclude that hi? mear&@slation_al-euergy.for the CHg? ion in~our-Ltidrk is-s~g&&tly.lower th& that-for .the~e$eriments of Harrison and-B&: -- : -.~~ .--- .:.'-I_ : -. :

I_ -_ ..-... .

. -;--. 'iid~iiu~10~~.~-----.-:_:. I -I--: ~1 :-_-:. .. --..:~-I... :-, 1 _~f_~: --y -~.__:~-_.~-~:_II:_: . -__~~ . :. -. .:_ -my _ .- .,--r-.m~-~ :_ .-m-I --~ --.----z;m;_ ~~_ .L l__-... .--. _I -_-~i6lrabiej aie-~-' ~'~'~~' -&e&,~<~~e rite ~~~~~~~~_messu;edinthis.stuay:but~__ ~.

_;

; ___ -.1. -;

I

. ‘not .ie_D~it~~~~~~~~~~l~~~~l~~~~~-,~_~~~~~is~~bl~~-~~~for~a~l~o~~~s-~~he~rate._~~ffici~~ts-__‘:;_; -:: :- -.&;3&. : ,._-.-. ___ +,_> .,., ;_ .: .-;z., Tr?< .;‘ -x9-;. C\+=‘~ g_. i .~epo&&for t&%&k ?-tie d&rived fro&: an_ass~~~_d$.@Ii ~~fil.~_~,~~~~~.~~_I-.cnl.-Il_ ; _&+,j&&~;~;;

.&Cl’

i’,‘;&g,,gti;,,

_

232,

~~ :

~~

,TtiLE::

.~-

RA7E COEFFICIENTS

MEASURED

IN

THIS

-~DY

&J-I

NOT

i.

Reactiqn

Reaction

INCLUDED _-

N20+-+CHc NzO+-+CH~ CH;+ +&O CHi* +NzO CHS+ +N,O CO, t +CH, co2 + +CH, CHi++COz

-+ products --~ +~C&+;ti& --t NOH+ +CHaN Y+ products --P NOH+ +dH;N -+ products - products : - C-%-CO z -+ products

TABLit-1

Td

1.17~0_07 _’ .0.08*0.04 ~0.006~ I .5&O-2 50.02 0.79&0.1 1.15*0.1 0.3*0.15 0.8&0.1

4~

5 -. -’ --.

ro*e+?f~ci?~* (&I3 &1&&-

Th& w&k

:N20’+CHk

IN

1 see- l x 109)J

._Orher mecisurt+nents

~. ~.

0.98f0.2b I:_ i _ -~.~ c 0.03f0.015~ 1.04f0.2b 0.03f0.015b

-.

-

I .07f0.09=, 2.3d -

...

-.

a Referred to a Glue of 1;22 for reaction (2), see text. bRef. 2.

-‘R&5. “Ref.

-_

~1

: ,

-_

...

1.

.I

-_

need further clarification. In many of the react&S the products: are unspe&fied The rate coefficient :k those cases represents the iurn of the rate~ko&%entsf&r -all possidle reaction pathways. For N20f and- CO,.: separate- mksuremeuts provide

rate coefficients

for the.elkctron

transcer

procksses.

:

’

Where combarisons .are possible in Table 5; the agreement is about as good as can be expected. It must be assumed that the rate coefficientfor reactive collision between COz+ aud methane reported by Kasper and_ Franklin is $r error .because of an under-estimation- of the ionic reaction time__ However for all of the other major rate coefficients;. satisfactory agreement is obtained :&ien the expizrimenti errors, _are considered. Thus -for. these ~exothcrmic processes, differences in. the __ internal--and translational energy~ of the ions; which- may,exist between the res_uhs cornpared,.,&ould ap$ar. to affect then rate coefficient .-by less km -15 %_ This finding:is in rnarked.contrast:to the ob&rvati&s for the endothermic reaction (18) whose -rate co&Ecient -appears to be. styqngly.- dependent upon ‘the. ex$er&nen& -~conditions~~ ---_ ~. :. .~ _I ._c ._-:- -. .-.yr_-~-~ ~_- _..~_--. ~. The only~major.dis~~~~cies. in Table 5 are for the kn& &actions&&h these-reactiorrsrender them c&e: produce _NOH ‘;-The_ io, rate c&t3@z&$‘for ‘&&ulingly~ more d~$Ecuh to I me&me -and’ it is possible that_ @e, error- lirr$s are greater-Tthan sho&&-l&ally likely l&&v& isrthat these &nor @ath$$ys’are~&ost ._ ;:_,I ~_-: : sensrttve to th&kne@ ‘carried into thi reactive:colIisidn,--y_~.~~ _~m-...

_

~._ _~ _. __ -._:- -~__ j

.’

: -_ ‘.

.~

..

. . __ ._1

.

. _ ,m~.I.

_._ ..I 21.3-,

~_10 F_ A._B%er=&d J: B_ H&ted, PM. Tr&_ ROY. Sac, A261 (1966) 33. -~ 11 ~,~P_:S&&r& z&d c_ O:Schissler, i..Chem. Ph&I, 29‘(1958) 282. -r -~ ., 12.:R. A. Flue&e, J_ Chem. &w.,~50 (1969) 4373. 13 J. H. I;utrell, J. Chein. P&s..59 (1973) $61_ _!4 w. T. Htit&% Jr and R .F_ Pjnizzhto, f. ~Chem;~Phys.,-59(l&3) 4?42: