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Efficiency of O2(1Σg+) formation by O(1D) + O2
Volume 9, number 3
CHEMICAL PHYSICS LETTERS
EFFICSEMCY
ad
OF
02&Z;)
FORMATION
1 Nay 1971
BY
O(‘ij)
+ 0,
‘D. R, SNELLING id M. GAUTHIER IlefeenseResearch ~s~~~~sh~e~~ Valcarfier Cedre tie Recherckes stw Ees atomes et les moMctttes, P.0.Bo.z 880, Caurcelelfe, P.Q. Canada l
Received 12 March 1971
The efficiency of formation of 0 (lC*) by energy transfer between O(lD) and 0, has been measured relative to the efficiency of O&J f or 18a t ion by photol~sis of ozone at 2587 A. ThG “Iwosinglet states of molecular oxygen were formed in a tlow system and their relative concentrations determiaed wit? a caffbrated detection system by measuring their emission at 7620 A and 1.27 /.I. The results show t??t if the cfficiendy of 02(lA,) formation by 02 photolysis is unity then the 1Zg state of 02 is produced in more than (85* 15) 5$ of the collisions deactivating O(lD). This determi~tion IS compared with previous re-
1. INTRODUCTION
cury lamps. The mean 03 and 02 pressures were respectively 0.046 torr and 10.9 torr and the fraction of 03 decomposed was typically 14%. The ozone was monitored with the use of an optical arrangement measuring the absorption of ultraviolet light at 2531 A. The cell was viewed axially by a Czerny-Turner spectrometer which enabled us to measure the intensity of the 7620 A and J-27 ~1emission bands by scanning in the 2nd and the 1st order of a 1.6 p grating respectively, aid measuring the area of each band Spectra of
In recent papers [l-4], a number of authors measured or astimated the probability of 04 (l +) production by energy transfer from 0(4”ri D) 4 ground state 02. It has been suggested [4,5] that this reaction could produce a good proportion of the 7620 k emission in the atmosphere but the efficiency of the 02#2 production is a matter of some discussion. &ad and Wayne [l], Noxon [3 3 and Young and Black [6] produced O$D) by 1470 31 photo&s& of 02. Izod and Wayne [l] studied the quenching of O(lD) by 02 and .concluded that one deactivation in 160 produces 02(I$). However Clark [2] has suggested that this result may be up to a factor of 50 loo’low and thus consistent with the work of Noxon who found the efficiency of 02(1X$ production to be greater than 0.3 and probably close to 1. Young and Black inferred qualitatively that the efficiency was close to 1. Indirect measurements using the Flash photolysls of ozone [4,7,8] strongly suggest a va!ue between 0.6 and 2. We have reinvestigated this reaction with a new approach and confirmed the higher efficiency for ,02(I g) formation.
nitrogen cooled RCA germanium photo~ode were used to detect the 7620 A and 1.27 g bands respectively and the relative sensitivity of these two detection systems was obtained using a G.E. type DXW-1000 watt quartz-iodine lamp calibrated by N.B.S. Radiatiqn from the standard lamp was diffused by an MgCO3 block, freshly coated with MgO, which was placed near the speotfometer slit.
,’
3; RESULTS AND DISCU~SICM
82. EXIJERIM?TAL
.
” $I a flow apparatus described previously [4,9], ozonimd oxygen from a Weisbach “Ozonator” &s passed th&ugh a quartz reaction vessbt fl-.
lrlrminated‘with qi& ~Hanov5.a141~ giresciure #&L4 :: ...,’ ,. ‘,,.-‘.
‘_
, ‘_
The reactions areasfollows: ‘. . .
of -im&tance :
‘.
in r&r. system :
met-
.’ ,.‘-
,,:-‘.‘..(’
-.,
\
;;
-
,”
‘_,. ,,
‘.-.
.‘.,
:
:
,.
I.“/_
.’
I
Volumd 9, number 3
CHEMICALFEiYSICSLETTERS
k2 O(lD) + 03 4 202,
Oh) + f$
(2)
k3 -+ O(3P) + 02(1 z; or 3 CL,,
02(lAg) + 03 3 202+0, k5 02(‘Ag) + 02 - 202, 02(lA,)
k6 + wall + 02,
02(q
t 03 k, 202 t 0.
The photolysis of 03 at 2537 A is known to produce O(ID) with a quantum yield c;f unity [IIIJ. From earlier work [4,9 with our system we have shown that the 02(, JAg) is formed by photolysis of 03, and the 02(1Zi)
wncentrafios 3.2. 02(‘4$ The rate constants for the reactions removing Oz(lAg) are kg = 2.2 X 10-18 [i5 IS]; kg = 0.2 t2 0.3 see-l [15] and kq = 3.5 Y 10ei5 ai: room temperature [1’7,18]. The temperature dependence of kq isin dispute [I?, 181 but this does not aKect the present work done at room temperature, md in any case we have measured the 02(lA ) lifetime (7) in our experiments using the tee5.nique described by Fir?dlay and Snelling [l?]. The reciprocal lifetime is given by l/7
(7)
by energy transfer
from O(lD) to 0,. Although it was found that 02(lAg) was not formed by energy transfer from O@D), we could not exclude ground state 02(3$) production, It was also shown that the relative rate of O(lD) removal by 03 and 02(k2/k3) is 9.7 [4]. 3 1 o#c+) concent7-cztion ’ ihe deagtivation of 02(1~t) by 02 or on the reaction vessel walls with raTe constants of 1 x 10-16 cm3 molecule-l see-1 111,121 and C 2 X 102 set-1 [4] respectively are negligible compared to deactivation of 02(fCi) by the reaction with 03 for which values of k7 of 2.5~10~11 [13] and 7 x lo-12 [14] have been obtained. (All rate cot-@ants will be in cm3 molecule-1 SeC-l unless otherwise stated.) The predominance of reaction (7) in removing 02(lXi) has been confirmed experimentally in our earlier publication [4]. With this reaction,scheme the steady state expression for the 02(lCz) concentratitin is
(8) where f is the fraction of the reactions between O(1D) and 02 which produce 02(lCi) and 4031 is the rate of 03 photoiysis. The expression in parenthesis in (8) above is the fraction of O(lD) atoms reacting with 02 and, for the experimental conditions we have used ([O2]/cO3],= 250), hti the value 0.96 and ii not ‘sensitive to small er,rors in &a/kg.
1 May L97l
= k&]
+ k5[02] + k6,
(9)
and the measured value of 1,‘~ of 7.0 * 0.2 set-l agrees with the value calculated from expression (9) above. With a linear flow rate of 21.2 cm see-1 the excited molecule takes at least 1 set to travel from the end of the iiluminaated region of the cell to the pumping outlet. The lifetime of the singlet states are close to 0.1 set for lAg and to iO-4 set for IZi for our conditions and there should be no pumping effect since the singlet oxygen molecules will be confined to the illuminated portion of the ceil. Nevertheless we investigated the possible effect of linear ELowrate on I h. Three different linear flow rates of 10.6, 21.3 and 42.3 cm set-1 were used and (l/cr - R5[02j) was observed to be constant to within * 4% for an 03 pressure of 0.043 torr. The steady state expression for 02(lAg) is then given by [02(‘Ag)]
= gJ[O3]‘i-,
where g is the fraction of 03 molecuies lysed which produce 02(lAg).
(10) photo-
3.3, Determinatiotr of the ratio f/g The ratio of (8) and (10) gives the expression
so that the ratio f/g can be obtained if [Ci~(~Ci)]j )] is known. This relative singlef. oxygen concen I ration can be determined from the measured relative intensities using the relationship: [Q(lA
I = NAIzv, where I is the inter&&, N is the number of excited molecules, A is the Einstein factor for spontaueous emission and kv the photon energy. Thu? [“dlz;)]
= 0.762 A(A) I(E)
[o&A,)]
1.27
A(z)Iw’
02)
25!i
. .’
Volume 9, number 3
CHEMICALPHYSICSLETTERS
where A(A) and A(Q are2.58x 30-d see-11191 ’ and’0.081 set-1 [5,20,2X] respectively. The experimentally determined ratioof the. The error is the standard deviation for a series of 8 experiments. Using this ratio and expressions (11) and (12) &ove with k7 = 2.5 x 10-11 a value of ,f/g of 0.89 rt 0.15 is obtained. If k7 = ‘7 x lo-12 is used then f/g = 0.25 f 0.09. Recent flash photolysis results in our laboratory 181 yield fi7 = (2.0 to 2.6: x 10-11confirming the higher value of k7. Thus we favour a value of f/g of 0.89 f 0.15 although a further 20% uncertainty is probably required to account for systematic errors in A(X) and A(A) giving f/g.=. 0.89+ 0.33. Jones and WaJine {22J have recently measured g, the quantum efficiency*for 02(IAg) formation by 03 photolysis at 2537 A, and found It to be unity. Fram our measurements f is thea also close to unity in accordance with the measurements of Noxon [3] and the flash photolysis resufts of Biedenkagp and Bair [7] and similar resuits obtained in the author’s laboratory [a] distissed in ref. f4J. These latter results we not in agreement with the lower efficiencies (f = l/180) obtained by Izod and Wayne 111. 3.4. Atmospheric iwzplications Our earlier results [4] have shown that approximately 30% of the O(ID) formed by solar photodissociat$on of 03 in tie atmosphere will be deactivated by 02. In the light of our present measurements f = 1, so that approximateiy 30% of the 03 photodissociation wilt also produce 02(1$). The predominant fate of atmospherically produced 02(1Cg) below 90 km is deactivation by N2 5J and the product of this deactivation may be 02( !l A ) rather than the ground state 02(12;-) [16,2$ Since the product of the solar ultra vf:olet photodissociation of 03 is O(1D) and 02(IAg) and since up to 30% of the O(lD> can evenhrally lead to indirect product!on of 02(lAg)
._‘_
.‘
,
.‘/ .:
,‘.
;.
i May l&l
then the effective quantum &Id of 02(lAg) ‘productioa may be 1.3 at all altitudes where 02(lC$ is deactivated (< 90 km).
REFERENCES fl] T.P. J.Izod and R. P. Wayne, Chem. Phys. Letters -4 (1969)
208.
[2] I. T?.Clark, Chem. Phys. Letters 6 (1970) 317. [3] J. I’.Noxon, J.Chem. Phys. 52 (1970) 1852. 141 M. Gauthier and D. R. SneUing, J. Cbem. Phys., to be _oublished. [S] L-Wallace and D. M. Hunten, J. Geophys. Res. 73 (1368) 4813. f6]_ R.A.Young and G.Black, J.Chem.Phys. 47 (1967) 2311. [7] D. Biedenkapp and E. J. Bair, 3. Chem.Phys. 52 (1970) 6119. 181 C. J. Fort& and D. R. Snelling, unpublished results; C. J. Fortin. M, SC. thesis, Universite de Montreal (1970). . IQ1M. Gauthier and D. R. Snelling, Chem. Phys. Letters 5 (197O} 93. PI W. 8. DeMore and 0. F. Raper, J. Chem. Phys. 44 (13X%)1780. F-11 S. 1’. Filseth, A. Zia’and K.H. Welge. J. Chem. Phys. 52 (1970) 5502. 1121E.C. Zipf, Can. J. Chem. 47 (1969) 1863. 1131 R. Gilpin, H. I. Sehiff and K. Welge. in preparation. Proc.Roy.Soc. A308 [141 T.P.3.IzodandR.J?.Wayne, (19dS) 81. II61 F. D. Findlay, C. J. Fortin and D. R. Sneliing, Chcm. Phys. Letters 3 (1969) 204. fI61 1. D. Clark and R. P. Wayne, Proc. Roy.Soc. A314 (19tiS) X11. J. Chem. Phys., 1171 F. D. Findlay and D. R.Snelling, td be published. WI 1. D.Clark, I. T.N. Jones and R.P. Wayne, Pro% Ro?_.Soc. A317 (1970) 407. J. 1191 R. Id-Badger, A.C. Wright and R. F.Wbitlock, Chem. Phys. 43 (1963) 4345. fzol J. H. Milier, R. W. Boese and L. P. Giver, J.Quant. Spectry.Radiatlve Transfer 9 (1969) 1507. 1211D. E. Burch and D.A. Gryvnak, Philco-Ford Corp., Tubl. no. W-4076 (1967). t221I. T. N. Jones and R. P. Wayne, Proc.Roy. Sot. A, to he published. IM.Kubo and E. A. Ogryzlo. Advaa. [231 S. J.Amold, Chem.Ser. 77 (1968) 1331
CHEMICAL PHYSICS LETTERS
EFFICSEMCY
ad
OF
02&Z;)
FORMATION
1 Nay 1971
BY
O(‘ij)
+ 0,
‘D. R, SNELLING id M. GAUTHIER IlefeenseResearch ~s~~~~sh~e~~ Valcarfier Cedre tie Recherckes stw Ees atomes et les moMctttes, P.0.Bo.z 880, Caurcelelfe, P.Q. Canada l
Received 12 March 1971
The efficiency of formation of 0 (lC*) by energy transfer between O(lD) and 0, has been measured relative to the efficiency of O&J f or 18a t ion by photol~sis of ozone at 2587 A. ThG “Iwosinglet states of molecular oxygen were formed in a tlow system and their relative concentrations determiaed wit? a caffbrated detection system by measuring their emission at 7620 A and 1.27 /.I. The results show t??t if the cfficiendy of 02(lA,) formation by 02 photolysis is unity then the 1Zg state of 02 is produced in more than (85* 15) 5$ of the collisions deactivating O(lD). This determi~tion IS compared with previous re-
1. INTRODUCTION
cury lamps. The mean 03 and 02 pressures were respectively 0.046 torr and 10.9 torr and the fraction of 03 decomposed was typically 14%. The ozone was monitored with the use of an optical arrangement measuring the absorption of ultraviolet light at 2531 A. The cell was viewed axially by a Czerny-Turner spectrometer which enabled us to measure the intensity of the 7620 A and J-27 ~1emission bands by scanning in the 2nd and the 1st order of a 1.6 p grating respectively, aid measuring the area of each band Spectra of
In recent papers [l-4], a number of authors measured or astimated the probability of 04 (l +) production by energy transfer from 0(4”ri D) 4 ground state 02. It has been suggested [4,5] that this reaction could produce a good proportion of the 7620 k emission in the atmosphere but the efficiency of the 02#2 production is a matter of some discussion. &ad and Wayne [l], Noxon [3 3 and Young and Black [6] produced O$D) by 1470 31 photo&s& of 02. Izod and Wayne [l] studied the quenching of O(lD) by 02 and .concluded that one deactivation in 160 produces 02(I$). However Clark [2] has suggested that this result may be up to a factor of 50 loo’low and thus consistent with the work of Noxon who found the efficiency of 02(1X$ production to be greater than 0.3 and probably close to 1. Young and Black inferred qualitatively that the efficiency was close to 1. Indirect measurements using the Flash photolysls of ozone [4,7,8] strongly suggest a va!ue between 0.6 and 2. We have reinvestigated this reaction with a new approach and confirmed the higher efficiency for ,02(I g) formation.
nitrogen cooled RCA germanium photo~ode were used to detect the 7620 A and 1.27 g bands respectively and the relative sensitivity of these two detection systems was obtained using a G.E. type DXW-1000 watt quartz-iodine lamp calibrated by N.B.S. Radiatiqn from the standard lamp was diffused by an MgCO3 block, freshly coated with MgO, which was placed near the speotfometer slit.
,’
3; RESULTS AND DISCU~SICM
82. EXIJERIM?TAL
.
” $I a flow apparatus described previously [4,9], ozonimd oxygen from a Weisbach “Ozonator” &s passed th&ugh a quartz reaction vessbt fl-.
lrlrminated‘with qi& ~Hanov5.a141~ giresciure #&L4 :: ...,’ ,. ‘,,.-‘.
‘_
, ‘_
The reactions areasfollows: ‘. . .
of -im&tance :
‘.
in r&r. system :
met-
.’ ,.‘-
,,:-‘.‘..(’
-.,
\
;;
-
,”
‘_,. ,,
‘.-.
.‘.,
:
:
,.
I.“/_
.’
I
Volumd 9, number 3
CHEMICALFEiYSICSLETTERS
k2 O(lD) + 03 4 202,
Oh) + f$
(2)
k3 -+ O(3P) + 02(1 z; or 3 CL,,
02(lAg) + 03 3 202+0, k5 02(‘Ag) + 02 - 202, 02(lA,)
k6 + wall + 02,
02(q
t 03 k, 202 t 0.
The photolysis of 03 at 2537 A is known to produce O(ID) with a quantum yield c;f unity [IIIJ. From earlier work [4,9 with our system we have shown that the 02(, JAg) is formed by photolysis of 03, and the 02(1Zi)
wncentrafios 3.2. 02(‘4$ The rate constants for the reactions removing Oz(lAg) are kg = 2.2 X 10-18 [i5 IS]; kg = 0.2 t2 0.3 see-l [15] and kq = 3.5 Y 10ei5 ai: room temperature [1’7,18]. The temperature dependence of kq isin dispute [I?, 181 but this does not aKect the present work done at room temperature, md in any case we have measured the 02(lA ) lifetime (7) in our experiments using the tee5.nique described by Fir?dlay and Snelling [l?]. The reciprocal lifetime is given by l/7
(7)
by energy transfer
from O(lD) to 0,. Although it was found that 02(lAg) was not formed by energy transfer from O@D), we could not exclude ground state 02(3$) production, It was also shown that the relative rate of O(lD) removal by 03 and 02(k2/k3) is 9.7 [4]. 3 1 o#c+) concent7-cztion ’ ihe deagtivation of 02(1~t) by 02 or on the reaction vessel walls with raTe constants of 1 x 10-16 cm3 molecule-l see-1 111,121 and C 2 X 102 set-1 [4] respectively are negligible compared to deactivation of 02(fCi) by the reaction with 03 for which values of k7 of 2.5~10~11 [13] and 7 x lo-12 [14] have been obtained. (All rate cot-@ants will be in cm3 molecule-1 SeC-l unless otherwise stated.) The predominance of reaction (7) in removing 02(lXi) has been confirmed experimentally in our earlier publication [4]. With this reaction,scheme the steady state expression for the 02(lCz) concentratitin is
(8) where f is the fraction of the reactions between O(1D) and 02 which produce 02(lCi) and 4031 is the rate of 03 photoiysis. The expression in parenthesis in (8) above is the fraction of O(lD) atoms reacting with 02 and, for the experimental conditions we have used ([O2]/cO3],= 250), hti the value 0.96 and ii not ‘sensitive to small er,rors in &a/kg.
1 May L97l
= k&]
+ k5[02] + k6,
(9)
and the measured value of 1,‘~ of 7.0 * 0.2 set-l agrees with the value calculated from expression (9) above. With a linear flow rate of 21.2 cm see-1 the excited molecule takes at least 1 set to travel from the end of the iiluminaated region of the cell to the pumping outlet. The lifetime of the singlet states are close to 0.1 set for lAg and to iO-4 set for IZi for our conditions and there should be no pumping effect since the singlet oxygen molecules will be confined to the illuminated portion of the ceil. Nevertheless we investigated the possible effect of linear ELowrate on I h. Three different linear flow rates of 10.6, 21.3 and 42.3 cm set-1 were used and (l/cr - R5[02j) was observed to be constant to within * 4% for an 03 pressure of 0.043 torr. The steady state expression for 02(lAg) is then given by [02(‘Ag)]
= gJ[O3]‘i-,
where g is the fraction of 03 molecuies lysed which produce 02(lAg).
(10) photo-
3.3, Determinatiotr of the ratio f/g The ratio of (8) and (10) gives the expression
so that the ratio f/g can be obtained if [Ci~(~Ci)]j )] is known. This relative singlef. oxygen concen I ration can be determined from the measured relative intensities using the relationship: [Q(lA
I = NAIzv, where I is the inter&&, N is the number of excited molecules, A is the Einstein factor for spontaueous emission and kv the photon energy. Thu? [“dlz;)]
= 0.762 A(A) I(E)
[o&A,)]
1.27
A(z)Iw’
02)
25!i
. .’
Volume 9, number 3
CHEMICALPHYSICSLETTERS
where A(A) and A(Q are2.58x 30-d see-11191 ’ and’0.081 set-1 [5,20,2X] respectively. The experimentally determined ratioof the. The error is the standard deviation for a series of 8 experiments. Using this ratio and expressions (11) and (12) &ove with k7 = 2.5 x 10-11 a value of ,f/g of 0.89 rt 0.15 is obtained. If k7 = ‘7 x lo-12 is used then f/g = 0.25 f 0.09. Recent flash photolysis results in our laboratory 181 yield fi7 = (2.0 to 2.6: x 10-11confirming the higher value of k7. Thus we favour a value of f/g of 0.89 f 0.15 although a further 20% uncertainty is probably required to account for systematic errors in A(X) and A(A) giving f/g.=. 0.89+ 0.33. Jones and WaJine {22J have recently measured g, the quantum efficiency*for 02(IAg) formation by 03 photolysis at 2537 A, and found It to be unity. Fram our measurements f is thea also close to unity in accordance with the measurements of Noxon [3] and the flash photolysis resufts of Biedenkagp and Bair [7] and similar resuits obtained in the author’s laboratory [a] distissed in ref. f4J. These latter results we not in agreement with the lower efficiencies (f = l/180) obtained by Izod and Wayne 111. 3.4. Atmospheric iwzplications Our earlier results [4] have shown that approximately 30% of the O(ID) formed by solar photodissociat$on of 03 in tie atmosphere will be deactivated by 02. In the light of our present measurements f = 1, so that approximateiy 30% of the 03 photodissociation wilt also produce 02(1$). The predominant fate of atmospherically produced 02(1Cg) below 90 km is deactivation by N2 5J and the product of this deactivation may be 02( !l A ) rather than the ground state 02(12;-) [16,2$ Since the product of the solar ultra vf:olet photodissociation of 03 is O(1D) and 02(IAg) and since up to 30% of the O(lD> can evenhrally lead to indirect product!on of 02(lAg)
._‘_
.‘
,
.‘/ .:
,‘.
;.
i May l&l
then the effective quantum &Id of 02(lAg) ‘productioa may be 1.3 at all altitudes where 02(lC$ is deactivated (< 90 km).
REFERENCES fl] T.P. J.Izod and R. P. Wayne, Chem. Phys. Letters -4 (1969)
208.
[2] I. T?.Clark, Chem. Phys. Letters 6 (1970) 317. [3] J. I’.Noxon, J.Chem. Phys. 52 (1970) 1852. 141 M. Gauthier and D. R. SneUing, J. Cbem. Phys., to be _oublished. [S] L-Wallace and D. M. Hunten, J. Geophys. Res. 73 (1368) 4813. f6]_ R.A.Young and G.Black, J.Chem.Phys. 47 (1967) 2311. [7] D. Biedenkapp and E. J. Bair, 3. Chem.Phys. 52 (1970) 6119. 181 C. J. Fort& and D. R. Snelling, unpublished results; C. J. Fortin. M, SC. thesis, Universite de Montreal (1970). . IQ1M. Gauthier and D. R. Snelling, Chem. Phys. Letters 5 (197O} 93. PI W. 8. DeMore and 0. F. Raper, J. Chem. Phys. 44 (13X%)1780. F-11 S. 1’. Filseth, A. Zia’and K.H. Welge. J. Chem. Phys. 52 (1970) 5502. 1121E.C. Zipf, Can. J. Chem. 47 (1969) 1863. 1131 R. Gilpin, H. I. Sehiff and K. Welge. in preparation. Proc.Roy.Soc. A308 [141 T.P.3.IzodandR.J?.Wayne, (19dS) 81. II61 F. D. Findlay, C. J. Fortin and D. R. Sneliing, Chcm. Phys. Letters 3 (1969) 204. fI61 1. D. Clark and R. P. Wayne, Proc. Roy.Soc. A314 (19tiS) X11. J. Chem. Phys., 1171 F. D. Findlay and D. R.Snelling, td be published. WI 1. D.Clark, I. T.N. Jones and R.P. Wayne, Pro% Ro?_.Soc. A317 (1970) 407. J. 1191 R. Id-Badger, A.C. Wright and R. F.Wbitlock, Chem. Phys. 43 (1963) 4345. fzol J. H. Milier, R. W. Boese and L. P. Giver, J.Quant. Spectry.Radiatlve Transfer 9 (1969) 1507. 1211D. E. Burch and D.A. Gryvnak, Philco-Ford Corp., Tubl. no. W-4076 (1967). t221I. T. N. Jones and R. P. Wayne, Proc.Roy. Sot. A, to he published. IM.Kubo and E. A. Ogryzlo. Advaa. [231 S. J.Amold, Chem.Ser. 77 (1968) 1331