Vibrational relaxation in the lowest electronically excited state of N2 in solid Kr and Xe

Vibrational relaxation in the A 3Σu+ state of N2 in rare gas matrices has been investigated by selective excitation with an excimer pumped and frequency doubled dye laser system combined with stimulated anti-Stokes Raman scattering. The relaxation is dominated at high N2 concentrations of some percent by nonresonant electronic energy transfer to other randomly distributed N2 molecules and at low concentrations by multiphonon processes. The relaxation by energy transfer can be described with the Förster–Dexter model and exchange interaction. Time resolved data are compared with calculated configuration averaged rate constants. The multiphonon processes can compete with energy transfer only if the N2–N2 spacings exceed several lattice constants. The multiphonon rate constants are comparable to the radiative ones in Kr but are much smaller than the radiative ones in Xe. The increase in radiative rate constants with vibrational quantum number is explained by a stronger mixing with the host excitons due to a better energy resonance.