Environmental effects on noble-gas hydrides: HXeBr, HXeCCH, and HXeH in noble-gas and molecular matrices.

Noble-gas hydrides HNgY (Ng is a noble-gas atom and Y is an electronegative group) are sensitive probes of local environment due to their relatively weak bonding and large dipole moments. We experimentally studied HXeBr in Ar, Kr, and N2 matrices, HXeCCH in Ne and N2 matrices, and HXeH in an N2 matrix. These are the first observations of noble-gas hydrides in an N2 matrix. An N2 matrix strongly increases the H-Xe stretching frequency of HXeBr and HXeCCH with respect to a Ne matrix, which is presumably due to a strong interaction between the HNgY dipole moment and quadrupole moments of the surrounding lattice N2 molecules. The spectral shift of HXeBr in an N2 matrix is similar to that in a CO2 matrix, which is a rather unexpected result because the quadrupole moment of CO2 is about three times as large as that of N2. The H-Xe stretching frequencies of HXeBr and HXeCCH in noble-gas matrices show a trend of ν(Ne) < ν(Xe) < ν(Kr) < ν(Ar), which is a non-monotonous function of the dielectric constants of the noble-gas solids. The MP2(full) calculations of HXeBr and HXeCCH with the polarizable continuum model as well as the CCSD(T) calculations of the HXeBr···Ng and HXeCCH···Ng (Ng = Ne, Ar, Kr, and Xe) complexes cannot fully explain the experimental observations. It is concluded that more sophisticated computational models should be used to describe these experimental findings.