RYDBERG STATES IN QUANTUM CRYSTALS NO IN SOLID H-2

Fluorescence, excitation and fluorescence depletion spectra of the low est Rydberg states of NO trapped in H-2 matrices are reported. The abs orption bands are shifted by about 0.58 eV to the blue of the gas phas e energy. They are strongly broadened and exhibit an asymmetry by a bl ue wing. The fluorescence bands are significantly narrower, with a red wing, and lie very close to the gas phase energy. The absorption line shape can be accounted for by the large extension of the ground state wavefunction, due to the strong contribution of the zero point motion in the H-2 lattice. The absorption-emission Stokes shift is interprete d in terms of 'bubble' formation around the Rydberg excited molecule. A moment analysis of the absorption and emission bands in the harmonic approximation shows that most of the absorption-emission Stokes shift is used up as energy to create the 'bubble' around the excited molecu le. The fluorescence depletion spectrum yields Rydberg-Rydberg transit ions very close to the gas phase energy. This, together with the fluor escence spectra, indicates that the molecule is in a quasi-free, gas-p hase-like state in the expanded cage. The excitation spectra and the f luorescence depletion spectra indicate a severe compression of the Ryd berg series of NO in H-2 matrices, which can be accounted for by a lar ge negative electron affinity of solid H-2. Concerning the intramolecu lar energy relaxation in NO, it is found that the Rydberg<->valence re laxation processes follow much the same pattern as observed in rare ga s matrices for the lower valence states. For the higher valence states , a photochemical route is suggested. For the vibrational relaxation b y Delta upsilon = 2 in the A state and for the C-A electronic relaxati on, intermolecular energy transfer processes between NO molecules are invoked, which occur in the sub-ns timescale.