Vibrational energy transfer from CO(v= 1), N2(v= 1), CO2(001), N2O(001) and OCS(001) to O3

Abstract

Rate constants have been determined for the relaxation of CO(v= 1), N₂(v= 1), CO₂(001), N₂O(001) and OCS(001) by O₃ at (295 ± 4) K, as follows: CO(v= 1)+O₃: k₃=(3.6^+0.1_–0.3)× 10^–13 cm³ molecule^–1 s^–1; N₂(v= 1)+O₃: k₆=(2.4^+0.7_–0.9)× 10^–14 cm³ molecule^–1 s^–1; CO₂(001)+O₃: k₇=(9.3 ± 0.4)× 10^–13 cm³ molecule^–1 s^–1; N₂O(001)+O₃: k₁₁=(2.8 ± 1.0)× 10^–13 cm³ molecule^–1 s^–1; OCS(001)+O₃: k₁₈=(1.7 ± 0.6)× 10^–12 cm³ molecule^–1 s^–1. The excited molecules were produced by electronic–vibrational (E–V) energy transfer from O(¹D) atoms created by laser flash photolysis of O₃, followed by rapid relaxation of molecules in levels higher than those specified. The rate constants for vibrational relaxation were determined by observing the variation of infrared fluorescence with time in gas mixtures of different composition.

The experiments have been accompanied by theoretical calculations using a modification of the Sharma–Brau theory for vibrational–vibrational (V–V) energy exchange. These indicate that the relaxation of CO(v= 1) by O₃, and probably of OCS(001) by O₃, occurs via V–V exchange with O₃ raised to its (101) level, whereas relaxation of CO₂(001) and N₂O(001) probably involves their transfer to (02°0) and promotion of O₃ to (001).