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

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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 \nu = 2; Omega = 1/2] vibronic component of the X(2)II 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 A(2) Sigma(+) - X(2)II(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 nu, j levels. The rotationally thermalized population in nu = 2 relaxes by vibration-vibration (V-V) energy exchange, NO(nu = 2) + NO(nu = 0) --> 2 NO(nu = 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

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