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The production of H(2S) atoms in the energy-transfer reaction of O2(1Δg) with HO2(X̃2A″)
Volume104, number1
THE PR0DUC~DN OF O&Ag)
OF H(‘S) ATOMS IN THE ENERGY-T~SFER
WITH NO@
23 January 1964
PHYSICSLETTERS
CHEMICAL
REACTION
2A*)
W. HACK and H. KURZKE Max-Planck-fnsritut fiir Str~mn,lgrforci~lcng, Bzifringerstrcsse 4-8. 3400 Giirringen,
West Gennaq
Received18 October 1983; in finalform 27 October 1983
The reaction of Oz(l A$ with H02@) was studied in an isothermal flow reactor in the pressure range 0.7
I _ Introduction
2. Experimental
Results obtained for the reaction of H atoms with electronically excited metastab‘le 02 molecules disagree substantially. Westenberg et al. [l] observed that fewer H atoms were consumed if a part of the 02 in his flow reactor was converted into Oz(lA&, and concluded that H atoms do not react with Oz(‘Ag). Other groups have found that H f 02(‘+) is a reasonably fast reaction [2,3]. In these experiments, the depletion of 02(lAg) molecules was observed in a flow system either by mass spectroscopy f2] or by an ESR-detection method [3]. This discrepancy could be due to physical quenching of 0~(lA~) by H atoms, but the system is more complicated since the reaction ofH atoms with 02f3Z;j nas to be considered. The purpose of this work is to examine the energytransfer reaction
The experimental arrangement is described in detail elsewhere f6]_ Only some essentials are mentioned here. A fast discharge-how system was used with resonance absorption (0, H atoms) and laser-induced-fluorescence (OH radicals) detection methods. The H atoms ([H]o i 1.5 X 10-l’ mol cmA3) were produced in a microwave discharge in a He/& mixture (Hz/He < 1 vol.%). The metastable O-, molecules (1.6 X 10B1*< fO2(‘q] S6 X lo-1Qmol cm-3) were obtaiz:ed in a microwave discharge in pure 02. The 0 atoms were destroyed on a mercury oxide surface [7] _ The O-atom concentration in the flow was smaller than 7.5 X I O-l5 mol cmm3; a statement which is limited by the sensitivity of the resonance absorption device. The experiments were carried out in the pressure range 0.7 Sp G 10.7 mbar and temperatures ranging from 300 to 423 IL The absolute concentrations are obtained in the titration reactions H + NO, and 0 + NO [S] _
O&Ad
i- HO@
2A’) -+ H(2S) + ~OZ(~ZF)
.
The electronically excited HO&$ produced in the fast reaction
?_A’) radicals are
O&a,)
‘A’)+ OZ(~Z<),
+- HO@
2A”) + HO&
Cl>
(2)
which was studied recently by Podolske and Johnston 143 and Glaschick-Sch&npf et al. [5]_ The highly vibrationally excited H02(X) may decompose to form H atoms and 02(3X;) molecules.
0 009-2614/84/$03.00 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
arrangement
3. Results The H-atom profiles were measured in the absence and presence of O,(lA& These results are shown in B.V.
93
CHEMICAL PHYSICS LEFRS
volume 104, number 1
27 January 1984
s-1P
84 0-l' 7-lo-u T 2
6=10-‘”
s L
5=lO-~
&lo-”
I
3*1o-n
2=1O-u l=lda
t
0
10
I
20
t
30
I
10
*
50
60
70
80
Fb 1. H-atom pr&Ies in the prcsencc end absence of q (’ A& Points correspond to measured values and I&es to
the computer!@mktion withthe rates give? %Itable f . lHfo = 1.X X lO-12 mol cm-, T? 297 K,p 7 5.3 mbar. 0 [Q,&3Zg)] 0 [O&g)]
= 6.2 X lo-’ = 6.2 X10-’
mol cxrT3, [O,(* A$] molcn~-~, [O#A$]
= 0; = 2.5 x
mol cmm3; A j@$Zj$] = 1.5 X 10e8 mol cmm3, [CW’Ag)] = O;n [%C3Q] = 15 X 10e8 mo! cmm3,
10-‘”
[*(‘AS)]
= 6.0 X lo-lo
mol cmW3_
ReaCth rate ~~~~zU’I~ Wed for
COmputer SiRluhtiOIl
Z0,<3zg)
the
A& Points correspond to measured v&es
+ 0, 02
and Iines to
computersimu.&ionwith the rates giveniu table 1. (Ex-
p&mental conditions are given in fii l_)
1 for one given set of experimental conditions. Fig. 1 shows that H atoms are produced if a small amount of ground-state 02 is excited to O#A&.
fig.
p = 5.3 m&r, T= 2gg j& M = He
- ISIOI this work this work 19,111
H+HOzCXZAO)-,H2+&(‘~~)
H+waU-,products -Ho, +_waII -, products OH +_wall-+prodacts O+waU-,products
%(I
Ref.
H+02<332 )+M-HO&X*AP)+M
H%~*A”)+ HOz(X2A%-+H2~ H%(1Y2A’I)+ 0H~*2n)-,HZO+ H~(A2A’)*M+H02(A2A8)+M M=He
Fig. 2.OH-radicaI profiIes in the presence and absence of
of the I-8and OHp&i&
Rfzaetion H~(X’A~*q(‘ng)-H9(A2A’)+q{3~~ J.%(A*A’)+ O#A&+_H(%)+ H+HCWX*A”)-,20H(X*II) ti+ H&(X2A”)-,H20+ O(jP)
t EmsI
SO
t rms1
Pm1 [9,111 WI [131 [Sl ISI ISI this work _ this wmk
this work this work
Volume 104. number 1
CHEMICAL
37 January
PHYSICS LETTERS
1984
ressure. This effect becomes smaher with increasing The addition of CO2 in the range l_ 1 X 1O- B g [CO,] < 4.6 X 10-9 mol crne3 infhrences the observed H-atom profdes. The OH-radicaI profiles obtained are illustrated in fig_ 2 for the same experimentaf conditions as in fig. 1. A decrease of the OH production is observed after addition of Oz(lA& This effect shows a similar pressure dependence as that for the H atoms, i.e. the effect becomes smaIIer with increasing pressure. The rate constant for reaction (1) was obtained by simulating the H and OH profiles. The value obtained
cm3 mol-’ s-l [4]. Th‘IS result differs from a recent publication by Glaschick-Schimpf et al. [S]. They observed the emission of HO& 2A’) populated in reaction (2) and evaluated a rate of k2 = (3: is;) X 1O’O cm3 mol- 1 s-l_ This value is about three orders of magnitude smaller than that obtained in ref. [4] _The authors suggest that two different channels may contribute to 02(‘&) depletion [S] :
iS
whereas only one of these channeIs leads to the formation of eIectronicaIly excited IIOz(x) [ 14-161 which is observed in IR emission. The contribution of thii work as far as reaction (2) is concerned is that H@(A) formed in reaction (2) is consumed by another O~(~dg) in reaction (1). This leads to the high rate observed by Podolske and Johnston and gives a low rate as far as the rate of production of HO& ‘A’) is measured by its emission. The value we bad to use in order to fit our OH and H profties was k2 = (1 -C0.5)X 1O1’ cm3 mold1 s-l. Of course, there is a strong interaction between the rate constants of (1) and (2). One cannot be varied without affecting the otber. So both rate constants have to be adjusted with respect to each other. The production of H atoms is explained by reactions (1) and (2). In the same way, the decrease in OH can be unde~toodThe consumption of HO? which is the main precursor for OH radicah in the system leads to a decrease in importance of reaction (4a). At higher pressures, deactivation of H02(A) becomes more important and thus the decomposition is less efficient; this explains the observed pressure effect. Reaction (1) also explains the contradictory observations for reaction (5) by those who observed the depletion of H atoms [l] and those groups who observed the 02(‘A,$ consumption [2,3]. It seems to be not only a matter of chemical reaction and/or quenching, but a more complicated mechanism than #at assumed until now_ If the mechanism proposed in this work is valis a Iimit for the heat of formation &&~k for HOz(X 2A’ O,O,O) of a26 kJ mol-’ is implied_
kl = (1 * 0.5) X 1014 cm3 mol-1 s-l _ The uncertainty of this value, mainly due to several assumptions in the mechanism, wilI be given in detail in the discussion section. In the temperature range examined no significant temperature dependence of the rates was observed_
4. Discussion The reaction
reaction
system is mainhy described of ground-state 02:
H(2S) + 02(3Z;) This reaction
by the
2 H02(% 2A”) .
(3)
is folIowed by
H+HO&+OH+OII,
(4a1
-+H~o+o.
(4b)
-+H2+02_
(4c)
The rate constants k3 and k+_c are known ]9,1 l], and simulation of the H and OH profiles in the ahsence of OS(~L\S) is possible. In the presence of 02(l&), the direct reaction of H atoms H + 02($)
--, 0H(211) + O(3P)
(5)
and the energy-transfer reactions (1) and (2) mentioned above have to be taken into account. The rate of reaction (5) has been determined independently. The rate of the resonant energy-transfer reaction (2) has been measured by PodoIske and Johnston [4] and by Glaschick-Schimpf et al. [S] . Simulating the ozone concentration in an 031H201He photolytic system, the authors obtained the value k2 = (2.0i 1.0) X 1013
O&A&
+ H0&2A”)
-+OZ(~Z;)
f- HO&
‘A’) _
95
Volume 104, number 1
CHEMICAL PHYSiCS LETTERS
Acknowledgement The hrthors are greatly jnd&ted to Professpi HGg. Wagner for his generous support. and stimtiating interest.
References 111 AA. Westenbe& 3-M. Roscoe and N. Dehaas, Chem. Phys Letters 7 (1970) 597, 121 _ - C. Schmidt and H-1. Schiff, Chem. Phyr Letters 23 (1973) 339. 133 LT. Cupitt, G.A. Takacs and G-P_ Glass, Intern. 3. Chem. Kinatics 14 (1982) 487. [4] JR. Podolske and H.S. Johnston, J. Phys Chem. 87 (1983) 629.. [S J I. Glaschick-Schimpf, W- Hans and U. Schurath, 84. Bunsentagung, Bielefeld (1983) f6f W. Ha&H. Kurzke and H.Gg Wagner, MPI fur St&mungsforschung, Bericht 2/1983.
96
27 January 1984
[ 7) C-W. Bader and B.A. Osznzlo- Discussions Faraday Sot. 37 {1964)-46. 181 hi.kk &ne.and LS. McDermid, J. Chem. Sot. Faraday Trans I71 (1975) 218% f9] W. Hack, K. Hoyermann and H.&r. Wagner, Ber. Bonsenges Physik. Chem; 82 (1978) 713. IlO] b.C. Baulch, D-D. Drysdale, D-G. Home and kc. Lloyd, Homoge&ous gas phase reactions of the H2-02 _systems (Butterwortbs, London, 1972). [ 111 V.C. Sridharan, C.X. Qiu and F. Kaufman, J. Phys Cbem. 86 (1982) 4569. [12] C.F.J. geyser, J. Phys Chem. 87 (1983) 837. 1131 W- Hack, A-W. Preuss and H.Gg. Wagner, Ber. Bunsenges Phyaik. Chem. 82 (1978) 1167. 1141 K-H. Becker, E.H. F&k, P. Langen and U. Schwa@ 2. Naturforsck 28a (19’73) 1872. [15] K.H. Becker, E.H. Fink, A. Leii and U. Schurath, Chem. Phyt Letters 59 (1977) 191, [16] HE. Hunziker and H.R. Wend& J. Chem. Phys 60 (1974) 4622.
THE PR0DUC~DN OF O&Ag)
OF H(‘S) ATOMS IN THE ENERGY-T~SFER
WITH NO@
23 January 1964
PHYSICSLETTERS
CHEMICAL
REACTION
2A*)
W. HACK and H. KURZKE Max-Planck-fnsritut fiir Str~mn,lgrforci~lcng, Bzifringerstrcsse 4-8. 3400 Giirringen,
West Gennaq
Received18 October 1983; in finalform 27 October 1983
The reaction of Oz(l A$ with H02@) was studied in an isothermal flow reactor in the pressure range 0.7
I _ Introduction
2. Experimental
Results obtained for the reaction of H atoms with electronically excited metastab‘le 02 molecules disagree substantially. Westenberg et al. [l] observed that fewer H atoms were consumed if a part of the 02 in his flow reactor was converted into Oz(lA&, and concluded that H atoms do not react with Oz(‘Ag). Other groups have found that H f 02(‘+) is a reasonably fast reaction [2,3]. In these experiments, the depletion of 02(lAg) molecules was observed in a flow system either by mass spectroscopy f2] or by an ESR-detection method [3]. This discrepancy could be due to physical quenching of 0~(lA~) by H atoms, but the system is more complicated since the reaction ofH atoms with 02f3Z;j nas to be considered. The purpose of this work is to examine the energytransfer reaction
The experimental arrangement is described in detail elsewhere f6]_ Only some essentials are mentioned here. A fast discharge-how system was used with resonance absorption (0, H atoms) and laser-induced-fluorescence (OH radicals) detection methods. The H atoms ([H]o i 1.5 X 10-l’ mol cmA3) were produced in a microwave discharge in a He/& mixture (Hz/He < 1 vol.%). The metastable O-, molecules (1.6 X 10B1*< fO2(‘q] S6 X lo-1Qmol cm-3) were obtaiz:ed in a microwave discharge in pure 02. The 0 atoms were destroyed on a mercury oxide surface [7] _ The O-atom concentration in the flow was smaller than 7.5 X I O-l5 mol cmm3; a statement which is limited by the sensitivity of the resonance absorption device. The experiments were carried out in the pressure range 0.7 Sp G 10.7 mbar and temperatures ranging from 300 to 423 IL The absolute concentrations are obtained in the titration reactions H + NO, and 0 + NO [S] _
O&Ad
i- HO@
2A’) -+ H(2S) + ~OZ(~ZF)
.
The electronically excited HO&$ produced in the fast reaction
?_A’) radicals are
O&a,)
‘A’)+ OZ(~Z<),
+- HO@
2A”) + HO&
Cl>
(2)
which was studied recently by Podolske and Johnston 143 and Glaschick-Sch&npf et al. [5]_ The highly vibrationally excited H02(X) may decompose to form H atoms and 02(3X;) molecules.
0 009-2614/84/$03.00 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
arrangement
3. Results The H-atom profiles were measured in the absence and presence of O,(lA& These results are shown in B.V.
93
CHEMICAL PHYSICS LEFRS
volume 104, number 1
27 January 1984
s-1P
84 0-l' 7-lo-u T 2
6=10-‘”
s L
5=lO-~
&lo-”
I
3*1o-n
2=1O-u l=lda
t
0
10
I
20
t
30
I
10
*
50
60
70
80
Fb 1. H-atom pr&Ies in the prcsencc end absence of q (’ A& Points correspond to measured values and I&es to
the computer!@mktion withthe rates give? %Itable f . lHfo = 1.X X lO-12 mol cm-, T? 297 K,p 7 5.3 mbar. 0 [Q,&3Zg)] 0 [O&g)]
= 6.2 X lo-’ = 6.2 X10-’
mol cxrT3, [O,(* A$] molcn~-~, [O#A$]
= 0; = 2.5 x
mol cmm3; A j@$Zj$] = 1.5 X 10e8 mol cmm3, [CW’Ag)] = O;n [%C3Q] = 15 X 10e8 mo! cmm3,
10-‘”
[*(‘AS)]
= 6.0 X lo-lo
mol cmW3_
ReaCth rate ~~~~zU’I~ Wed for
COmputer SiRluhtiOIl
Z0,<3zg)
the
A& Points correspond to measured v&es
+ 0, 02
and Iines to
computersimu.&ionwith the rates giveniu table 1. (Ex-
p&mental conditions are given in fii l_)
1 for one given set of experimental conditions. Fig. 1 shows that H atoms are produced if a small amount of ground-state 02 is excited to O#A&.
fig.
p = 5.3 m&r, T= 2gg j& M = He
- ISIOI this work this work 19,111
H+HOzCXZAO)-,H2+&(‘~~)
H+waU-,products -Ho, +_waII -, products OH +_wall-+prodacts O+waU-,products
%(I
Ref.
H+02<332 )+M-HO&X*AP)+M
H%~*A”)+ HOz(X2A%-+H2~ H%(1Y2A’I)+ 0H~*2n)-,HZO+ H~(A2A’)*M+H02(A2A8)+M M=He
Fig. 2.OH-radicaI profiIes in the presence and absence of
of the I-8and OHp&i&
Rfzaetion H~(X’A~*q(‘ng)-H9(A2A’)+q{3~~ J.%(A*A’)+ O#A&+_H(%)+ H+HCWX*A”)-,20H(X*II) ti+ H&(X2A”)-,H20+ O(jP)
t EmsI
SO
t rms1
Pm1 [9,111 WI [131 [Sl ISI ISI this work _ this wmk
this work this work
Volume 104. number 1
CHEMICAL
37 January
PHYSICS LETTERS
1984
ressure. This effect becomes smaher with increasing The addition of CO2 in the range l_ 1 X 1O- B g [CO,] < 4.6 X 10-9 mol crne3 infhrences the observed H-atom profdes. The OH-radicaI profiles obtained are illustrated in fig_ 2 for the same experimentaf conditions as in fig. 1. A decrease of the OH production is observed after addition of Oz(lA& This effect shows a similar pressure dependence as that for the H atoms, i.e. the effect becomes smaIIer with increasing pressure. The rate constant for reaction (1) was obtained by simulating the H and OH profiles. The value obtained
cm3 mol-’ s-l [4]. Th‘IS result differs from a recent publication by Glaschick-Schimpf et al. [S]. They observed the emission of HO& 2A’) populated in reaction (2) and evaluated a rate of k2 = (3: is;) X 1O’O cm3 mol- 1 s-l_ This value is about three orders of magnitude smaller than that obtained in ref. [4] _The authors suggest that two different channels may contribute to 02(‘&) depletion [S] :
iS
whereas only one of these channeIs leads to the formation of eIectronicaIly excited IIOz(x) [ 14-161 which is observed in IR emission. The contribution of thii work as far as reaction (2) is concerned is that H@(A) formed in reaction (2) is consumed by another O~(~dg) in reaction (1). This leads to the high rate observed by Podolske and Johnston and gives a low rate as far as the rate of production of HO& ‘A’) is measured by its emission. The value we bad to use in order to fit our OH and H profties was k2 = (1 -C0.5)X 1O1’ cm3 mold1 s-l. Of course, there is a strong interaction between the rate constants of (1) and (2). One cannot be varied without affecting the otber. So both rate constants have to be adjusted with respect to each other. The production of H atoms is explained by reactions (1) and (2). In the same way, the decrease in OH can be unde~toodThe consumption of HO? which is the main precursor for OH radicah in the system leads to a decrease in importance of reaction (4a). At higher pressures, deactivation of H02(A) becomes more important and thus the decomposition is less efficient; this explains the observed pressure effect. Reaction (1) also explains the contradictory observations for reaction (5) by those who observed the depletion of H atoms [l] and those groups who observed the 02(‘A,$ consumption [2,3]. It seems to be not only a matter of chemical reaction and/or quenching, but a more complicated mechanism than #at assumed until now_ If the mechanism proposed in this work is valis a Iimit for the heat of formation &&~k for HOz(X 2A’ O,O,O) of a26 kJ mol-’ is implied_
kl = (1 * 0.5) X 1014 cm3 mol-1 s-l _ The uncertainty of this value, mainly due to several assumptions in the mechanism, wilI be given in detail in the discussion section. In the temperature range examined no significant temperature dependence of the rates was observed_
4. Discussion The reaction
reaction
system is mainhy described of ground-state 02:
H(2S) + 02(3Z;) This reaction
by the
2 H02(% 2A”) .
(3)
is folIowed by
H+HO&+OH+OII,
(4a1
-+H~o+o.
(4b)
-+H2+02_
(4c)
The rate constants k3 and k+_c are known ]9,1 l], and simulation of the H and OH profiles in the ahsence of OS(~L\S) is possible. In the presence of 02(l&), the direct reaction of H atoms H + 02($)
--, 0H(211) + O(3P)
(5)
and the energy-transfer reactions (1) and (2) mentioned above have to be taken into account. The rate of reaction (5) has been determined independently. The rate of the resonant energy-transfer reaction (2) has been measured by PodoIske and Johnston [4] and by Glaschick-Schimpf et al. [S] . Simulating the ozone concentration in an 031H201He photolytic system, the authors obtained the value k2 = (2.0i 1.0) X 1013
O&A&
+ H0&2A”)
-+OZ(~Z;)
f- HO&
‘A’) _
95
Volume 104, number 1
CHEMICAL PHYSiCS LETTERS
Acknowledgement The hrthors are greatly jnd&ted to Professpi HGg. Wagner for his generous support. and stimtiating interest.
References 111 AA. Westenbe& 3-M. Roscoe and N. Dehaas, Chem. Phys Letters 7 (1970) 597, 121 _ - C. Schmidt and H-1. Schiff, Chem. Phyr Letters 23 (1973) 339. 133 LT. Cupitt, G.A. Takacs and G-P_ Glass, Intern. 3. Chem. Kinatics 14 (1982) 487. [4] JR. Podolske and H.S. Johnston, J. Phys Chem. 87 (1983) 629.. [S J I. Glaschick-Schimpf, W- Hans and U. Schurath, 84. Bunsentagung, Bielefeld (1983) f6f W. Ha&H. Kurzke and H.Gg Wagner, MPI fur St&mungsforschung, Bericht 2/1983.
96
27 January 1984
[ 7) C-W. Bader and B.A. Osznzlo- Discussions Faraday Sot. 37 {1964)-46. 181 hi.kk &ne.and LS. McDermid, J. Chem. Sot. Faraday Trans I71 (1975) 218% f9] W. Hack, K. Hoyermann and H.&r. Wagner, Ber. Bonsenges Physik. Chem; 82 (1978) 713. IlO] b.C. Baulch, D-D. Drysdale, D-G. Home and kc. Lloyd, Homoge&ous gas phase reactions of the H2-02 _systems (Butterwortbs, London, 1972). [ 111 V.C. Sridharan, C.X. Qiu and F. Kaufman, J. Phys Cbem. 86 (1982) 4569. [12] C.F.J. geyser, J. Phys Chem. 87 (1983) 837. 1131 W- Hack, A-W. Preuss and H.Gg. Wagner, Ber. Bunsenges Phyaik. Chem. 82 (1978) 1167. 1141 K-H. Becker, E.H. F&k, P. Langen and U. Schwa@ 2. Naturforsck 28a (19’73) 1872. [15] K.H. Becker, E.H. Fink, A. Leii and U. Schurath, Chem. Phyt Letters 59 (1977) 191, [16] HE. Hunziker and H.R. Wend& J. Chem. Phys 60 (1974) 4622.