INTERDEPENDENCE OF GUEST RADIATIONLESS TRANSITIONS AND LOCALIZED PHONON STRUCTURE: NH AND ND ($A^{3}\Pi$) IN RARE GAS LATTICES

Abstract

NH and ND ($A^{3}\Pi$) radicals in rare gas lattices were studied by their time and wavelength resolved fluorescence. The temperature dependence of the localized phonon structure indicates that the ground $X^{3}\Sigma^{-}$ state undergoes near free rotation, while the excited $A^{3}\Pi$ state librates. A strong violation of the energy gap law for vibrational relaxation is observed with NH rates 10$-10^{2}$ higher than in ND. The vibrational relaxation rates are independent of temperature for $T < 25 ^{\circ} K$ in Ar and $< 37 ^{\circ} K$ in Kr; however, lifetimes of several $A^{3}\Pi$ vibrational levels show a dramatic temperature dependence attributed to intersystem crossing into $^{1}\Delta$. We propose that the localized near free rotation mode accepts the energy during vibrational relaxation, while delocalized Lattice phonons accept energy during intersystem crossing.