The photolysis of SO 2 at 3130 Å in the presence of cis ‐ and trans ‐2‐pentene

The photolysis of SO 2 at 3130 Å, FWHM = 165 Å, and 22°C has been investigated in the presence of cis ‐ and trans ‐2‐pentene. Quantum yields for the SO 2 photosensitized isomerization of one isomer to the other have been made for a variation in the [SO 2 ]/[C 5 H 10 ] ratio of 3.41–366 for cis ‐2‐C 5 H 10 and of 1.28–367 for trans ‐2‐C 5 H 10 . A kinetic analysis of each of these systems permitted new estimates to be made for the SO 2 collisionally induced intersystem crossing ratio at 3130 Å from SO 2 ( 1 B 1 ) to SO 2 ( 3 B 1 ). The estimates of k 1a /( k 1a + k 1b ) obtained are 0.12 ± 0.01 and 0.12 ± 0.02 (two different kinetic analyses in the cis ‐2‐C 5 H 10 study) and 0.20 ± 0.05 and 0.20 ± 0.04 (two different kinetic analyses in the trans ‐2‐C 5 H 10 study). Collisionally induced intersystem crossing ratios of k 2a /( k 2a + k 2b ) = 0.51 ± 0.10 and k 3a /( k 3a + k 3b ) = 0.62 ± 0.12 were obtained for cis ‐ and trans ‐2‐pentene, respectively. Quenching rate constants at 22°C for removal of SO 2 ( 3 B 1 ) molecules by cis ‐ and trans ‐2‐C 5 H 10 were estimated as (1.00 ± 0.29) × 10 11 l./mole·sec and (0.857 ± 0.160) × 10 11 l./mole/sec, respectively. Prolonged irradiations, extrapolated to infinite irradiation times, for mixtures initially containing SO 2 and pure isomer, either the cis or trans , yielded a photostationary composition of [ trans ‐2‐pentene]/[ cis ‐2‐pentene] = 2.1 ± 0.1.