Spectroscopic studies of the Ar(H-2)(2) compound crystal at high pressure and low temperatures

Fourier-transform infrared and Raman studies are performed on Ar(H-2)(2) co mpound single crystals over a large pressure (5-30 GPa) and temperature (30 -300 K) range in a diamond-anvil cell. The effect of polarization on the in frared absorption is investigated. On the basis of the spectroscopic featur es and comparing to the cases of purl solid H-2 and of matrix isolated H-2 in argon crystal, we assign the quite complex infrared spectra to the pure vibron and vibron plus phonons acid vibron plus rotons combination bands. T he difference of the infrared and Raman vibron frequency, as a function of pressure, is interpreted quantitatively with reference to vibrational coupl ing between hydrogen molecules, as in the hydrogen crystal case. Informatio n on the structural properties can thus be derived. Finally, this study hig hlights the similarity in the molecular problems for the Ar(H-2)(2) compoun d and for solid hydrogen. [S0163-1829(99)12529-3].