Vibrational relaxation and electronic energy transfer of N 2 aggregates in solid Xe matrices

Abstract

Population distributions of vibrational levels within the first excited electronic state A 3 Σ u + of N 2 molecules embedded in a Xe matrix have been derived from emission spectra resulting from selective excitation of individual levels with monochromatized synchrotron radiation. The steady-state population distributions strongly depend on the originally excited level and are incompatible with a simple stepwise nonradiative relaxation process between successive vibrational levels. The experimental distributions are attributed to relaxation by nonradiative electronic energy transfer processes between neighbouring N 2 molecules via exchange interaction. The cascade in the A 3 Σ u + state involves relaxation to lower energies in steps of two vibrational quanta and an up conversion of the energy in steps of three vibrational quanta. The probability of these processes follows an energy gap law for the excess energy.