- Email: [email protected]
Kinetics of the reaction of CF3O2 with NO
CHEMICAL
~ohunc 91, numbsr 3
KINETICS OF THE REACTION OF CF,O,
22 October 1982
PHYSICS LETTERS
WITH NO
1 C. PLUMB and K.R. RYAN
Rcccwcd 13 July 1982
The rare cocificwn ior the rcact~on oiCF,02 with NO has been mcasurcd at 295 R m hcbum usins 3 ilow tube nmplcd by 2 rnxs spcctromurcr The KIIUC obrlmed ior this raw coeiircicnt was (17 8 f 3 6) x IO-‘* crK3 s-t and iound to bc indcpcndcnr of [Hc] over the range (6 3-16 8) x lOI cmm3.Tbls value is 3pproulmxcly 3 ixtur of 2 higher than carher measurcmcnts of the rate cociiictcnts ior CH,O, and C2HS02 with NO and mdic;ltes that further measurements arc rcquued for this lmportzmt cbss of rzxtions
the present work CF,02 radicals were produced by the reaction
1. hroduction lntercs.1 UI the gas-phase rcnctions of pero.u> radicals
F -I- CF3H
stems from the fact that these species play rmportant roles !n atmospheric and combustion chemistry [ 1,I!]. It is also apparent that these species may play a sigrnficant role in the plasma etchmg of semiconductors used m the microelecrromcs mdustry [3] _ In the polluted atmosphere, the ovldatlon of NO to NO? by the reaction RO1 +NO+NO,
+RO
236
f HF,
CF, + 0, -. CF,O,
(3)
and consumed by the reaction CF30, + NO -+ CFgO + NO,.
(4)
F atoms were generated by passing 1% CFJ in He through a microwave discharge located In a 1 cm i.d.
ISan importam step m the production of ozone. When R = H [4], CH3 [5] and C?Hs [6], measurcments have shown that the rate coefkcients for the reactions described by (1) are considerably higher than preGous studlcs had suggested and have established the importance of these reactions For other peroxy radicals however. no duect measurements of the rate coefficients for the reaction with NO have been made. We report here a direct measurement of the rafe coefficient for the reaction between CFJOI and NO.
The reactIon was stuched at 7-95 K in a flow reactor sampled by a quadrupole mass spectrometer. A detaded description of this apparatus has been reported [7] _In
CF3
followed by
(1)
1. Experimental
-
Al203 side arm, 20-30
cm upstream from the entry
point to the main tlow
tube. Gas emergmg from the discharge was dduted =lOlM-fold by the main helium flow which entered the gas stream ~10 cm downstream from the discharge. Earlier measurements showed that when the main helium flow bypasses the chscharge in this way, Ihe discharge products CF, and CF? fall to undetectable levels before entermg the main flow Iube [g] _At the same time sufficient F atoms survive to participate in reactions further downstream. The SUMVing F atoms were consumed by CF3H which was added along with 02 5 cm downstream from the pomt of entry of the main hehum flow. Typical concentrations in the main flow tube were 1.5 X 1015 cm-3 for CFJH and 6.2 X lOI cm-I for OZ. For all measurements the flow velocity was “11 m s-l and reactions (2) and (3) were allowed to proceed for at least 50 cm in the main flow
0 009-2614/82/0000-0000/o/s
02.75 0 1982 North-Holland
tube before NO was added. Given the rate coefficient for reaction
(2) [9], and a value of 6 X lo-13 cm3 s-l
for reactron (3) for a typical [lo],
[He] of 6.3 X 1016 cme3
it IS clear that all the F atoms had been removed
and all the CF3 converted tion of NO. The [He]
to CF307 before the addi-
was within
th; range (6 3-16.8)
Nitric oxide, purified through
as described earlier [6] was
a movable
stream from the nuting CF3H.
In order to inhibit
inlet SO-80
cm down-
pomt of the F with 0, and the loss of radicals at the
walls, all surfaces m the flow reactor were coated with H3P04
to iollow
the decay of the CF30-,
correspondmg was switched
to CF70: - _ (m/e 83) when the discharge off. Thus residual signal corresponded to
*1.5% of the total signal at this mass number
the 02 and the He all contributed
this resrdual signal. Some contrlbutron be due to long-hved the electron
metastable
perouy
radrcak
detectable fragment
[I 11, CF30z
was found not to have a
parent ion in its mass spectrum. However a Ion CF?Oz was detected and this was used
m the rcagcnt gases
and reactron trmc sufficient to an undetcctablc
oif wassubtracted
made at this mass number hg.
to reduce
level, the w/e 82 sig-
from that measured with the
discharge ofi. Accordmgly [6] and the thrcz butyl
m
mcnts showed that, with the drscharge on and a combr-
discharge with CaH50,
to
neutrals producsd
In any event. repeated mcssurc-
nal was indrstinguishable
In common
to
is cxpecrcd
beam while mlpuritrcs
may also contribute.
the [CF,OJ
3. Results and discussion
uhcn the
drschargc was on but the NO flow was off. Tests showed
natlon oi [NO]
and baked in air at 500 K
In the flow tube. A
residual signal could be detected at the mass number
that the CF3H,
x 10’6 cm-3. admitted
1, Octobsr 198,
CHEMICAL PHYSICS LlTTERS
Volume 92. number 3
the m/e 82 srgnal with the from each mcasuremcnt
with the discharge on.
I shows typrcal decay curkcs for CFJO~ after
corrections
for the resrdual signal have been made. In
fig. 2. k,, the pseudo-first-order rate coefficient IS plotted against [NO]. The rcsulrs shown in fig 1 hn\c been corrected for diffusiatl effects as described carkr 171. These correcttons ranged from 0 Olk,,, to O.OW, and were typlcally
~0.034,.
Corrcctlons
have also
been made to the restdts m fig I! to allow for the amount of NO consumed. For the range of [NO]
shown in fig.
7- the measured consumption of NO at the longest rcxtion tune ranged irom 75 at llrs lowest [NO]
Reactton
Length
to 1.5%
km)
Fig. I. CF302 s~gnslas 3 iunction oir~c~~on length for [Hc] = 6.3 x lOI cmm3 and wvcral dlrfercnt vAucs ol [NO I. Conrhtlons (a) [NO] = I%9 x lOI cmm3,(b) [NO] = 7.54 x lOI2 cmm3.(c) [NO) =4 84 x lOI cm-“. (d) [NO] = 2.53 x IO’* cmm3.Results(a) and (d) were obtlmcd wth Ihc ?- I8 cmI d. flow rubc 11 a mean hncar flaw velocity of 10.8 m s-’ , (3) and (c) were obkmxd with the 1.0 cm I d. flow tube on a mean lmcar flow vclocrly oi 10.0 m s-l”.
FI: 1 X-+ 3s 3 funcrmn oi [NO]. Values shown35 clorcd CUCICS oblamcd wth 2. I8 cm i d ilow tube. open cuclcsobGnd Hlrh I.0 cm id wbc 237
Volume 91. number 3
CHEhIlCAL
PHYSICS LETTERS
22 October 1982
at the highest [NO] _The effect of NO consumption on the measured k, was computed for each k,, and rangsd
4. Conclusion
from 0.5% to 4% and was typically 2% The mfluenc2 oi wall eifects on the measured ke was
‘h2 value obtamsd fork, is approxunately a factor of 3- higher than earher m2asurements for the rate coef-
mvestlgated by usmg on2 flow tub2 of 7.18 cm i-d. and another of I 00 cm 1.d The results in fig. 2 show the ~11~2s of A-,, for both flow tub2s (2.18 cm closed circles, 1.00 cm open cmzles). For the 2.13 cm flow tube measurements with the NO flow oii raealrd that the
tkents for the reactions of CH302 and CzH~02 with NO made with the same apparatus. Clsarly, further 2x-
CF,O-, slgnal was mdependent of the position of the movable inlet. For the smaller flow tube the CF302 signal Increased as the movable inlet was withdrawn when the NO flow was off. Separate measurements of th2 addltional loss of CF302 du2 to the presrnce of the movable inlet were then used to correct the observed decay of the CF302 when the NO was flowing. Th2 magmtude of this correctton to k, was dependent on the value of k, and ranged from 10% for the smallest k, to 7-5% for the largest. These corrections have been mad2 to th2 results shown in fig. 3-. Analysis of the results from each tube taken separately shows that the rzsults are not statistically diff2rent and that the results m fig. 7- can b2 expressed ask, = k, [NO] with k, II-Idependent of [He] wthin the range (6 3- 16 8) X 10’6 cm-x. Th2 slope of th2 hne m !ig. 2 8iv2s a value fork, of (17.8 f 0.6) X 1O-12 cm3 s-l with 90% confidence Iunits. When uncsrtaintiss in [NO] and those arising from uncertamtles in gas flow are taken into account a total uncertainty of O.& IS obtatned yielding a rate coefficient oi (17 8 + 3.6) X 13-l? cm3 s-l.
138
psrimsnts are rrquired to estabhsh the deprndence of the rate coefficient for reaction (1) on the nature of R.
References [ 11 K.L. Demer]ian, J.A. Kerr and J G. Cr~lrsn. Advan 171 [3] [J] 151 161 [7] 181 191
En-
vuon. SCI.TcchnoL 1(1974) 1. S W. Benson, J. Phys. Chem. 85 (1981) 3375. C.J. Mopsb, A.C. Adams and D.L. Fhmm, J. Appl
Phys. 49 (1978) 3796. CJ Howard and K.hl. Evcnson.Gcophys. Rcs. Lctterj 1(1977) 437. I.C. Plumb, K.R. Ryan, J.R.Stckcnand h1.F.R hlulcahy, J. Phys Chcm. 85 (1981) 3136. I.C. Plumb, K.R. Ryan, J.R. Stcvcn and hi F.R. Muluhy, lntcrn J. Chcm. ~metxs I-1 (1982) 183. I.C. Plumb and K.R Ryan, Intern. J. Chcm. Kinctlcs 13 (1981) 1011. LC. Plumb and K R R>an, Intern. J. Chem. Kmerlcs. IO be published. T-L Polloch and W.E Jones, Can J. Chcm. 51 (1973) 2041.
[ 101 E R Ryan and I.C. Plumb. unpublished results
[ 11J T.hf.
Lcnhudt, C.E hlcDadc and K.D. Bsycj, J. Chem. Phyr 72 (1980) 301.
~ohunc 91, numbsr 3
KINETICS OF THE REACTION OF CF,O,
22 October 1982
PHYSICS LETTERS
WITH NO
1 C. PLUMB and K.R. RYAN
Rcccwcd 13 July 1982
The rare cocificwn ior the rcact~on oiCF,02 with NO has been mcasurcd at 295 R m hcbum usins 3 ilow tube nmplcd by 2 rnxs spcctromurcr The KIIUC obrlmed ior this raw coeiircicnt was (17 8 f 3 6) x IO-‘* crK3 s-t and iound to bc indcpcndcnr of [Hc] over the range (6 3-16 8) x lOI cmm3.Tbls value is 3pproulmxcly 3 ixtur of 2 higher than carher measurcmcnts of the rate cociiictcnts ior CH,O, and C2HS02 with NO and mdic;ltes that further measurements arc rcquued for this lmportzmt cbss of rzxtions
the present work CF,02 radicals were produced by the reaction
1. hroduction lntercs.1 UI the gas-phase rcnctions of pero.u> radicals
F -I- CF3H
stems from the fact that these species play rmportant roles !n atmospheric and combustion chemistry [ 1,I!]. It is also apparent that these species may play a sigrnficant role in the plasma etchmg of semiconductors used m the microelecrromcs mdustry [3] _ In the polluted atmosphere, the ovldatlon of NO to NO? by the reaction RO1 +NO+NO,
+RO
236
f HF,
CF, + 0, -. CF,O,
(3)
and consumed by the reaction CF30, + NO -+ CFgO + NO,.
(4)
F atoms were generated by passing 1% CFJ in He through a microwave discharge located In a 1 cm i.d.
ISan importam step m the production of ozone. When R = H [4], CH3 [5] and C?Hs [6], measurcments have shown that the rate coefkcients for the reactions described by (1) are considerably higher than preGous studlcs had suggested and have established the importance of these reactions For other peroxy radicals however. no duect measurements of the rate coefficients for the reaction with NO have been made. We report here a direct measurement of the rafe coefficient for the reaction between CFJOI and NO.
The reactIon was stuched at 7-95 K in a flow reactor sampled by a quadrupole mass spectrometer. A detaded description of this apparatus has been reported [7] _In
CF3
followed by
(1)
1. Experimental
-
Al203 side arm, 20-30
cm upstream from the entry
point to the main tlow
tube. Gas emergmg from the discharge was dduted =lOlM-fold by the main helium flow which entered the gas stream ~10 cm downstream from the discharge. Earlier measurements showed that when the main helium flow bypasses the chscharge in this way, Ihe discharge products CF, and CF? fall to undetectable levels before entermg the main flow Iube [g] _At the same time sufficient F atoms survive to participate in reactions further downstream. The SUMVing F atoms were consumed by CF3H which was added along with 02 5 cm downstream from the pomt of entry of the main hehum flow. Typical concentrations in the main flow tube were 1.5 X 1015 cm-3 for CFJH and 6.2 X lOI cm-I for OZ. For all measurements the flow velocity was “11 m s-l and reactions (2) and (3) were allowed to proceed for at least 50 cm in the main flow
0 009-2614/82/0000-0000/o/s
02.75 0 1982 North-Holland
tube before NO was added. Given the rate coefficient for reaction
(2) [9], and a value of 6 X lo-13 cm3 s-l
for reactron (3) for a typical [lo],
[He] of 6.3 X 1016 cme3
it IS clear that all the F atoms had been removed
and all the CF3 converted tion of NO. The [He]
to CF307 before the addi-
was within
th; range (6 3-16.8)
Nitric oxide, purified through
as described earlier [6] was
a movable
stream from the nuting CF3H.
In order to inhibit
inlet SO-80
cm down-
pomt of the F with 0, and the loss of radicals at the
walls, all surfaces m the flow reactor were coated with H3P04
to iollow
the decay of the CF30-,
correspondmg was switched
to CF70: - _ (m/e 83) when the discharge off. Thus residual signal corresponded to
*1.5% of the total signal at this mass number
the 02 and the He all contributed
this resrdual signal. Some contrlbutron be due to long-hved the electron
metastable
perouy
radrcak
detectable fragment
[I 11, CF30z
was found not to have a
parent ion in its mass spectrum. However a Ion CF?Oz was detected and this was used
m the rcagcnt gases
and reactron trmc sufficient to an undetcctablc
oif wassubtracted
made at this mass number hg.
to reduce
level, the w/e 82 sig-
from that measured with the
discharge ofi. Accordmgly [6] and the thrcz butyl
m
mcnts showed that, with the drscharge on and a combr-
discharge with CaH50,
to
neutrals producsd
In any event. repeated mcssurc-
nal was indrstinguishable
In common
to
is cxpecrcd
beam while mlpuritrcs
may also contribute.
the [CF,OJ
3. Results and discussion
uhcn the
drschargc was on but the NO flow was off. Tests showed
natlon oi [NO]
and baked in air at 500 K
In the flow tube. A
residual signal could be detected at the mass number
that the CF3H,
x 10’6 cm-3. admitted
1, Octobsr 198,
CHEMICAL PHYSICS LlTTERS
Volume 92. number 3
the m/e 82 srgnal with the from each mcasuremcnt
with the discharge on.
I shows typrcal decay curkcs for CFJO~ after
corrections
for the resrdual signal have been made. In
fig. 2. k,, the pseudo-first-order rate coefficient IS plotted against [NO]. The rcsulrs shown in fig 1 hn\c been corrected for diffusiatl effects as described carkr 171. These correcttons ranged from 0 Olk,,, to O.OW, and were typlcally
~0.034,.
Corrcctlons
have also
been made to the restdts m fig I! to allow for the amount of NO consumed. For the range of [NO]
shown in fig.
7- the measured consumption of NO at the longest rcxtion tune ranged irom 75 at llrs lowest [NO]
Reactton
Length
to 1.5%
km)
Fig. I. CF302 s~gnslas 3 iunction oir~c~~on length for [Hc] = 6.3 x lOI cmm3 and wvcral dlrfercnt vAucs ol [NO I. Conrhtlons (a) [NO] = I%9 x lOI cmm3,(b) [NO] = 7.54 x lOI2 cmm3.(c) [NO) =4 84 x lOI cm-“. (d) [NO] = 2.53 x IO’* cmm3.Results(a) and (d) were obtlmcd wth Ihc ?- I8 cmI d. flow rubc 11 a mean hncar flaw velocity of 10.8 m s-’ , (3) and (c) were obkmxd with the 1.0 cm I d. flow tube on a mean lmcar flow vclocrly oi 10.0 m s-l”.
FI: 1 X-+ 3s 3 funcrmn oi [NO]. Values shown35 clorcd CUCICS oblamcd wth 2. I8 cm i d ilow tube. open cuclcsobGnd Hlrh I.0 cm id wbc 237
Volume 91. number 3
CHEhIlCAL
PHYSICS LETTERS
22 October 1982
at the highest [NO] _The effect of NO consumption on the measured k, was computed for each k,, and rangsd
4. Conclusion
from 0.5% to 4% and was typically 2% The mfluenc2 oi wall eifects on the measured ke was
‘h2 value obtamsd fork, is approxunately a factor of 3- higher than earher m2asurements for the rate coef-
mvestlgated by usmg on2 flow tub2 of 7.18 cm i-d. and another of I 00 cm 1.d The results in fig. 2 show the ~11~2s of A-,, for both flow tub2s (2.18 cm closed circles, 1.00 cm open cmzles). For the 2.13 cm flow tube measurements with the NO flow oii raealrd that the
tkents for the reactions of CH302 and CzH~02 with NO made with the same apparatus. Clsarly, further 2x-
CF,O-, slgnal was mdependent of the position of the movable inlet. For the smaller flow tube the CF302 signal Increased as the movable inlet was withdrawn when the NO flow was off. Separate measurements of th2 addltional loss of CF302 du2 to the presrnce of the movable inlet were then used to correct the observed decay of the CF302 when the NO was flowing. Th2 magmtude of this correctton to k, was dependent on the value of k, and ranged from 10% for the smallest k, to 7-5% for the largest. These corrections have been mad2 to th2 results shown in fig. 3-. Analysis of the results from each tube taken separately shows that the rzsults are not statistically diff2rent and that the results m fig. 7- can b2 expressed ask, = k, [NO] with k, II-Idependent of [He] wthin the range (6 3- 16 8) X 10’6 cm-x. Th2 slope of th2 hne m !ig. 2 8iv2s a value fork, of (17.8 f 0.6) X 1O-12 cm3 s-l with 90% confidence Iunits. When uncsrtaintiss in [NO] and those arising from uncertamtles in gas flow are taken into account a total uncertainty of O.& IS obtatned yielding a rate coefficient oi (17 8 + 3.6) X 13-l? cm3 s-l.
138
psrimsnts are rrquired to estabhsh the deprndence of the rate coefficient for reaction (1) on the nature of R.
References [ 11 K.L. Demer]ian, J.A. Kerr and J G. Cr~lrsn. Advan 171 [3] [J] 151 161 [7] 181 191
En-
vuon. SCI.TcchnoL 1(1974) 1. S W. Benson, J. Phys. Chem. 85 (1981) 3375. C.J. Mopsb, A.C. Adams and D.L. Fhmm, J. Appl
Phys. 49 (1978) 3796. CJ Howard and K.hl. Evcnson.Gcophys. Rcs. Lctterj 1(1977) 437. I.C. Plumb, K.R. Ryan, J.R.Stckcnand h1.F.R hlulcahy, J. Phys Chcm. 85 (1981) 3136. I.C. Plumb, K.R. Ryan, J.R. Stcvcn and hi F.R. Muluhy, lntcrn J. Chcm. ~metxs I-1 (1982) 183. I.C. Plumb and K.R Ryan, Intern. J. Chcm. Kinctlcs 13 (1981) 1011. LC. Plumb and K R R>an, Intern. J. Chem. Kmerlcs. IO be published. T-L Polloch and W.E Jones, Can J. Chcm. 51 (1973) 2041.
[ 101 E R Ryan and I.C. Plumb. unpublished results
[ 11J T.hf.
Lcnhudt, C.E hlcDadc and K.D. Bsycj, J. Chem. Phyr 72 (1980) 301.