Nonradiative Rydberg↔valence relaxation of NO trapped in Ar, Kr, and Xe matrices

Abstract

Electronic and vibrational relaxation of NO in Ar, Kr and Xe matrices has been studied using excitation spectra and time and energy resolved emission spectra. In addition to the vibrationally relaxed emissions from a 4Π(v=0), B 2Π(v=0) and A 2Σ+(v=0) in Ar and Kr matrices, B(v=5 and 7) emissions are observed in Ar matrices. In Xe matrices, only Rydberg A 2Σ+(v=0) fluorescence is observed. Nonradiative Rydberg–valence transitions are observed in all matrices and valence–Rydberg transitions only in Ar matrices. The intensity ratios IA/IB/Ia are ∼3/9/88 in Ar, ∼9/3/88 in Kr, and ∼2–5/0/0 in Xe matrices. The quantum efficiency for total luminescence being near unity in Ar and Kr matrices. The branching ratios for intramolecular relaxation between Rydberg and valence states are described in terms of a model which combines the intramolecular Franck–Condon factors with the spectroscopically determined phonon Franck–Condon factors and solvent enhanced spin–orbit matrix elements. The latter increase from Ar to Xe matrices. This increase is rationalized in terms of a semiempirical model for the heavy-atom effect on spin–orbit mixing. Weak Rydberg–Rydberg relaxation by a Δv=2 step in Ar and a Δv=1 step in Kr is also observed and interpreted in terms of a resonant Förster–Dexter-type energy transfer. Finally in Xenon matrices, a strongly nonresonant energy transfer from the n=l exciton of solid xenon to the A(v=0) Rydberg level is observed.