QUENCHING AND RELAXATION OF VIBRATIONAL LEVELS OF NH/ND(A(1)DELTA,UPSILON)

The kinetics of the removal of vibrational levels of NH and ND in the metastable (a1DELTA) state, was investigated for collisions with the parent molecules HN3, HNCO, DN3, and DNCO and with N2 and O2. The parent molecules exhibit neither isotope effects nor a dependence of the removal rates on the vibrational levels. Opposite isotope effects were observed for N2 and O2; the rates become larger for N2 and smaller for O2 upon deuteration. For both O2 and N2, the rate constants increase with increasing vibrational excitation. In the case of N2, levels with v > 0 are barely electronically quenched but efficiently relaxed most likely in DELTAv = -1 steps to lower vibrational levels. The marked decrease in the quenching efficiency upon vibrational excitation is in qualitative agreement with efficient mixing of the N-H stretch with the other vibrational modes in the N2-NH complex and the Landau-Zener description of diabatic crossing of potential energy surfaces. Rate constants are estimated for the electronic quenching and vibrational relaxation processes.