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: −12; He: −12; N₂: −13; Ar: −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.