Intermolecular transfer of vibrational energy in matrix isolated NO. High vibrational states, electronic excitation and dissociation

Abstract

Nitric oxide dispersed in solid argon and krypton is vibrationally excited by a cw modulated infrared laser resonant with the fundamental or first overtone absorption. The energy deposited into ν = 1 or ν = 2 is redistributed to higher levels by intermolecular vibration to vibration transfer. The vibrational population distributions obtained from overtone emission spectra in both IR and visible regions or probed using a pulsed dye laser extend over a broad range. The topmost detected level is ν = 27. In addition to the vibrational fluorescence, electronic luminescence emanating from the lowest excited valence states a 4Π and B 2Π of NO is found to be induced by IR laser irradiation. The slow irreversible decay of the electronic emissions followed by thermoluminescence shows that a small fraction of the NO molecules is dissociated. Time and frequency resolved analysis of the various emissions is performed as a function of the relevant parameters. The results show that X 2Π→a 4Π intersystem crossing and X 2Π→B 2Π internal conversion do not occur in matrix isolated NO. A new mechanism of intermolecular vibrational to electronic energy transfer involving the exchange “en bloc” of a large number of vibrational quanta between highly vibrationally excited molecules is proposed. The excitation of NO to predissociated vibronic levels of the B 2Π state results in electronic emission and dissociation.