Vibrational Relaxation of SO(X³Σ^-, v = 1−5) and Nascent Vibrational Distributions of SO Generated in the Photolysis of SO₂ at 193.3 nm

Abstract

Rate coefficients for deactivation of SO(X 3 Σ -, V ) 1-5) by collisions with SO 2 and nascent vibrational populations in V ) 0-2 in the photolysis of SO 2 at 193.3 nm have been determined. A single vibrational level of SO(X 3 Σ -) was detected with laser-induced fluorescence (LIF) excited via the B 3 Σ --X 3 Σsystem. Time-dependent profiles of LIF signals were recorded as a function of the pressures of SO 2 . Observed profiles were analyzed by the integrated-profiles method and reproduced well by convolution calculations. Overall rate coefficients for vibrational relaxation of SO(V) by SO 2 have been determined to be (4.7 ( 0.5) × 10 -12 (V ) 1), (6.7 ( 0.4) × 10 -12 (V ) 2), (7.2 ( 0.7) × 10 -12 (V ) 3), (6.1 ( 1.0) × 10 -12 (V ) 4), and (8.6 ( 0.7) × 10 -12 (V ) 5) in units of cm 3 molecule -1 s -1 (the quoted errors are 2σ). We have also found that 63% of the vibrational deactivations of V ) 2 by SO 2 are governed by double-quantum relaxation: (4.2 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 for V ) 2 f V ) 0 and (2.5 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 for V ) 2 f V ) 1. Ab initio calculations enable us to find two stable complexes: OS-OSO and SO-SO 2 , indicating that attractive interactions play a significant role in the relaxation. The nascent vibrational distributions of SO have been measured to be 0.52 ( 0.1/0.75 ( 0.1/1.0 for V ) 0/1/2. The differences in vibrational distributions reported by bulk and beam experiments are attributed to the difference in the temperature of parent SO 2 .

Vibrational relaxation of O2(X 3 Σ–g, v = 9–13) by collisions with O2

“…Their value, k O 3 11 ¼ 9 Â 10 À14 cm 3 molecule À1 s À1 , can be used as an upper limit of k O 3 10 , and consequently, the lower limit of k Ar 10 is estimated to be E5 Â 10 À16 cm 3 molecule À1 s À1 . The observed profiles are fit by the following convolution integral 34 based on the linear-response theory: 35…”

Efficient vibrational relaxation of O2(X3Σ−g, ν = 8) by collisions with CF4

“…If some part of n = 8 is generated from n = 10 and/or higher vibrational levels, the plot shows a negative curvature. 40 However, it should be noted that there are two circumstances where the plots are linear even with non-zero probability for n , is estimated to be B5 Â 10 À15 cm 3 molecule À1 s À1 on the assumption that k diff is negligibly small.…”

“…We have also fit the observed profiles using the following convolution integral 40 based on the linear-response theory: 41…”

The B 3Σ− state of the SO radical

“…DFWM spectra to v 0 = 3-9 of the B-X transition of SO were recorded. Transitions observed using DFWM mostly originated from the v 00 = 2 level of the X state, due to the non-Boltzmann distribution of SO produced from the SO 2 photolysis [19]. The rotational temperature could be adjusted by adjusting the experimental geometry, with values around 100 K being typical.…”