Temperature dependence of the collisional energy transfer of OH(v=10) between 220 and 310 K

The temperature dependence of the thermally averaged collisional removal cross section of OH (X 2∏, v=10) by O2, N2O, and CO2 is measured between 220 and 310 K using a two-laser pump–probe technique and a specially designed vacuum-isolated flow cell. OH molecules are generated in v=6–9 by the reaction of hydrogen atoms and ozone. The (10,7) vibrational transition is excited with pulsed near-infrared laser light to create a population of OH (v=10) molecules. The temporal evolution of the v=10 population is monitored as a function of collider gas pressure by a time-delayed ultraviolet laser pulse. The probe step uses laser-induced fluorescence by exciting the B 2∑+–X 2∏ (0,10) transition and detecting the fluorescence from the B 2∑+–A 2∑+ (0,6–8) transitions. From 310 to 223 K, the OH (v=10) removal cross section increases by 35±21, 33±14, and 58±48 percent for the colliders O2, N2O, and CO2, respectively. This inverse temperature dependence is typical of a loss mechanism governed by long-range attractive forces.