Abstract
The chemiluminescent reaction between sulphur monoxide (SO) and ozone has been studied in a fast flow system at pressures between 0·3 and 3·0 mmHg, These species undergo a rapid bimolecular reation (1) SO + O
3
= SO
2
+ O
2
+ 106 kcal/mole (1) to yield ground state products, where
k
1
= 1·5 x 10
12
exp ( –2100/
RT
) cm
3
mole
-1
s
-1
. This reaction also yields electronically excited SO
2
molecules in the
1
B
and
3
B
1
states. The
1
B
SO
2
molecules are produced with up to 16 kcal/mole vibrational energy. Emission from the longer lived
3
B
1
state is vibrationally relaxed and provides no information about the initial energy distribution. Comparison with fluorescence studies shows that the
3
B
1
SO
2
molecules are produced mainly by collisional quenching of SO
2
molecules formed in the
1
B
state. The formation of electronically excited SO
2
is also a simple bimolecular process, but it involves a higher energy barrier than formation of ground state SO
2
. Our measurements on the chemiluminescence, when combined with data on the quenching of the SO
2
fluorescence, yield the rate constants
k
1a
= 10
11
exp ( – 4200/
RT
) and
k
lb
≯ 3 x 10
10
exp ( –3900/
RT
) cm
3
mole
-1
s
-1
for the bimolecular reactions SO + O
3
= SO
2
(
1
B
) + O
2
+ 21 kcal/mole, (1
a
) SO + O
3
= SO
2
(
3
B
1
) + O
2
+ 35 kcal/mole (1
b
) which form electronically excited SO
2
. No electronically excited O
2
appears to be formed. It is deduced that electronically excited SO
2
is produced by crossing to a separate potential surface at or near the transition state rather than by the formation of a highly vibrationally excited SO
2
molecule which crosses to the excited electronic state.
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