Collision dynamics of OH(X 2Π, v=9)

Abstract

Collisional removal rate constants for the OH(X 2Π, v=9) radical are measured for the colliders O2, CO2, and N2O and upper limits are established for He, H2, Ar, and N2. OH(v=6) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to v=9 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the v=9 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 B 2Σ+–X 2Π(0,9) transition and the resulting visible B 2Σ+–A 2Σ+ fluorescence is detected with a filtered photomultiplier tube. We measure rate constants for N2O: (6.4±1.0)×10−11; CO2: (5.7±0.6)×10−11; O2: (1.7±1.1)×10−11; H2: <3×10−12; He: <2×10−12; N2: <5×10−13; Ar: <2×10−13 (all in units of cm3 s−1). For O2 and CO2 these rate constants are significantly faster than those for low vibrational levels and comparable to those for v=12.