Infrared–ultraviolet double resonance measurements on the temperature dependence of rotational and vibrational self-relaxation of NO(X2Π, υ = 2,j)

Abstract

Infrared–ultraviolet double resonance experiments have been performed to measure the rates of rotational and vibrational self-relaxation in NO at three temperatures: 295 K, 200 K, and 77 K. Pulses of tunable infrared radiation from an optical parameteric oscillator have been used to excite molecules into selected rotational levels (j = 0.5, 6.5, or 15.5) in the [Formula: see text] vibronic component of the X2Π electronic ground state of NO. Loss of population from the initially excited level was observed by making time-resolved laser-induced fluorescence measurements on appropriate lines in the A2Σ+ − X2Π(2,2) band. The rate constants for removal of population from specific rovibronic levels are essentially independent of j and at 295 K agree well with previous direct measurements on a range of υ, j levels. The rotationally thermalized population in υ = 2 relaxes by vibration–vibration (V–V) energy exchange, NO(υ = 2) + NO(υ = 0) → 2 NO(υ = 1), at a rate which is almost independent of temperature and which seems to be uninfluenced by the presence of spin-orbit degeneracy in, and attractive forces between, the NO collision partners.