HXeI and HXeH in Ar, Kr, and Xe matrices: experiment and simulation.

Experimental and theoretical studies of HXeI and HXeH molecules in Ar, Kr, and Xe matrices are presented. HXeI exhibits the H-Xe stretching bands at 1238.0 and 1239.0 cm(-1) in Ar and Kr matrices, respectively, that are blue-shifted from the HXeI band observed in a Xe matrix (1193 cm(-1)) by 45 and 46 cm(-1). These shifts are larger than those observed previously for HXeCl (27 and 16 cm(-1)) and HXeBr (37 and 23 cm(-1)); thus, the matrix effect is stronger for less stable molecules. The results for HXeI are qualitatively different from all previous results on noble-gas hydrides with respect to the frequency order between Ar and Kr matrices. For previously studied HXeCl, HXeBr, and HXeCCH, the H-Xe stretching frequency is reliably (by >10 cm(-1)) higher in an Ar matrix than in a Kr matrix. In contrast, the H-Xe stretching frequency of HXeI in an Ar matrix is slightly lower than that in a Kr matrix. HXeH absorbs in Ar and Kr matrices at 1203.2 and 1192.1 cm(-1) (the stronger band for a Kr matrix), respectively. These bands are blue-shifted from the stronger band of HXeH in a Xe matrix (1166 cm(-1)) by 37 and 26 cm(-1), and this frequency order is the same as observed for HXeCl, HXeBr, and HXeCCH but different from HXeI. The present hybrid quantum-classical simulations successfully describe the main experimental findings. For HXeI in the 〈110〉 (double substitution) site, the order of the H-Xe stretching frequencies (ν(Xe) < ν(Ar) < ν(Kr)) is in accord with the experimental observations, and also the frequency shifts in Ar and Kr matrices from a Xe matrix are well predicted (30 and 34 cm(-1)). Both in the theory and experiment, the order of the H-Xe stretching frequencies differs from the case of HXeCl, which suggests the adequate theoretical description of the matrix effect. For HXeH in the 〈100〉 (single substitution) site, the order of the frequencies is ν(Xe) < ν(Kr) < ν(Ar), which also agrees with the experiments. The calculated frequency shifts for HXeH in Ar and Kr matrices with respect to a Xe matrix (36 and 23 cm(-1)) are in a good agreement with the experiments. The present calculations predict an increase of the H-Xe stretching frequencies in the noble-gas matrices with respect to vacuum.