The collisional quenching of I(5 2P [formula omitted]) by the molecules H 2O, CH 3OH, C 2H 5OH, HCOOH and CH 3COOH by time-resolved emission (I(5 2P [formula omitted]) → I(5 2P [formula omitted]) + hν, λ = 1.315 μm) following pulsed-laser photolysis

Abstract

The collisional quenching of electronically excited iodine atoms, I(5p 5( 2P 1 2 )), by the molecules H 2O, CH 3OH, C 2H 5OH, HCOOH and CH 3COOH was investigated directly in the time domain. I( 2P 1 2 ) was generated by the pulsed excimer laser photolysis of C 3F 7I at λ = 248 nm and monitored by time-resolved emission at λ = 1.315 μm (I( 2P 1 2 → I( 2P 3 2 ) + hν). Absolute second-order quenching rate constants ( k Q), including those for the collisional removal of the excited atom by the dimers (HCOOH) 2 and (CH 3COOH) 2, were obtained for room temperature. The following results were obtained: k Q per cm 3 mol −1 s −1 H 2O (2.1 ± 0.2) × 10 −12 CH 3OH (9.4 ± 0.9) × 10 −13 C 2H 5OH (14.6 ± 1.3) × 10 −13 HCOOH (3.5 ± 0.3) × 10 −13 (HCOOH) 2 (3.5 ± 0.4) × 10 −13 CH 3COOH (5.4 ± 0.5) × 10 −13 (CH 3COOH) 2 (5.4 ± 0.6) × 10 −13 These results indicate that the main route for removal is the electronic energy transfer in the iodine atom to the second vibrational level in the OH stretching mode in each case, via long-range attractive forces, probably involving dipole-quadrupole interaction on collision.