Electronic to vibrational energy transfer and relaxation in matrices. I. Hg in N2 matrix

Under KrF laser (249 nm) excitation of Hg atoms in a N₂ matrix in the temperature range 12–25 K we observed (i) a strong, broad-band fluorescence in the near-UV region assigned to a (Hg-N₂)^* exciplex (decay time from 800 to 100 μs) and (ii) infrared Δυ = −1 emission from high vibrational levels (υ = 6−12) of N₂ molecules in the electronic ground state, populated by the electronic-to-vibrational energy transfer (decay time 7 s on υ = 10−12 at 14 K). From time-resolved UV and IR spectra, one can conclude that the predominant part of the EV transfer takes place from thermally non-equilibrated levels, on a short time scale. This is unexpected in view of gas phase data and preliminary ab initio potential energy surface calculations. Temperature effects are discussed. Excited N₂ levels decay along a radiative path (predominant for the highest levels) and by VV transfer to N₂(υ=0) molecules with a rate decreasing rapidly with υ but strongly increasing with the sample temperature.