On the à and B̃ electronic states of NCO and its clusters with nonpolar solvents

Abstract

The B̃←X̃ and Ã←X̃ transitions of the NCO radical and its clusters with nonpolar solvents are studied in a supersonic jet expansion by employing laser-induced fluorescence techniques. Fluorescence excitation (FE) and hole burning spectra are recorded for the NCO radical and compared to previous work. NCO is clustered with Ar, N2, CH4, and CF4 nonpolar molecules to elucidate the effect of solvation on the radical energy levels and dynamics. FE spectra are detected for NCO 1:1 clusters showing blue shifts in their spectra with respect to that of the isolated NCO radical, while their 1:n counterparts show either red or blue shifts. Potential energy surface calculations are performed to evaluate the binding energies and geometries of 1:1 clusters in the X̃, Ã, and B̃ electronic states. The relatively long decay lifetime and red shifted fluorescence wavelength range observed for B̃ state clusters suggests that they decay first through internal conversion (IC) to à vibronic levels, and then experience rapid intracluster vibrational redistribution (IVR) and vibrational predissociation (VP), yielding ground state solvent molecules and NCO radicals at lower à vibronic levels. These à state NCO radicals subsequently emit, generating the Ã→X̃ band.