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

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 108; no. 13; pp. 2382 - 2388
• Main Authors: Yamasaki, Katsuyoshi, Taketani, Fumikazu, Sugiura, Kazuyuki, Tokue, Ikuo, Tsuchiya, Kentaro
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.04.2004
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp037333d

Rate coefficients for deactivation of SO(X3Σ-, v = 1−5) by collisions with SO2 and nascent vibrational populations in v = 0−2 in the photolysis of SO2 at 193.3 nm have been determined. A single vibrational level of SO(X3Σ-) was detected with laser-induced fluorescence (LIF) excited via the B3Σ-−X3Σ- system. Time-dependent profiles of LIF signals were recorded as a function of the pressures of SO2. 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 SO2 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 cm3 molecule-1 s-1 (the quoted errors are 2σ). We have also found that 63% of the vibrational deactivations of v = 2 by SO2 are governed by double-quantum relaxation:  (4.2 ± 0.9) × 10-12 cm3 molecule-1 s-1 for v = 2 → v = 0 and (2.5 ± 0.9) × 10-12 cm3 molecule-1 s-1 for v = 2 → v = 1. Ab initio calculations enable us to find two stable complexes:  OS−OSO and SO−SO2, 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 SO2.