Collisional removal of OH (X 2Π,ν=7) by O2, N2, CO2, and N2O

Abstract

Collisional removal rate constants for the OH (X 2Π,ν=7) radical are measured for the colliders O2, CO2, and N2O, and an upper limit is established for N2. OH(ν=4) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to ν=7 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the ν=7 population is probed as a function of the collider gas partial pressure by a time-delayed pulsed ultraviolet laser. The probe laser light is resonant with the (0,7) band of the B 2Σ+−X 2Π transition. Fluorescence from the B 2Σ+ state is detected in the visible spectral region. We measure rate constants for CO2, (6.7±1.0)×10−11; N2O, (3.0±0.6)×10−11; O2, (7±2)×10−12; and N2, <6×10−13 (all in units of cm3 s−1).