Structure and dynamics in pure and doped rare-gas matrices

Abstract

Far-i.r (f.i.r.) and inchoherent inelastic neutron scattering (INS) spectra of H₂O isolated in solid Ar and Kr have been interpreted in terms of essentially free single-particle rotation. On th other hand, rotating H₂O molecules are a sensitive probe for characterizing matrix effects. The related hindrance potentials within the matrix cage do not only cause lineshifts and line broadening, but also induce optically forbidden rotational transitions (ΔJ= 2).

The long-range order of Ar and Kr matrices and, inherently, the dimensions of the cage acting as host for H₂O are significantly influenced by (a) the conditions of vapour deposition and (b) the addition of N₂ to the matrix. These effects are monitored on the same sample by neutron diffraction and neutron spectroscopy (INS), respectively, using a tripel-axis spectrometer. The diffraction pattern clearly characterizes the type and extent of order present in the matrix. The spectroscopic data, on the other hand, lend themsleves to a reliable description of the hindrance potential acting on the isolated probe molecules.