Investigations of pure rotational transitions of H2 self-perturbed and perturbed by He. I. Measurement, modeling, and quantum calculations

Experimental and theoretical analysis of the rotational Raman spectrum of hydrogen molecules in clathrate hydrates

The Raman spectra of H(2) and HD molecules in simple hydrogen and binary hydrogen-tetrahydrofuran clathrate hydrates have been measured at temperatures as low as 20 K. The rotational bands of trapped molecules in simple and binary hydrates have been analyzed, and the contributions originating from hydrogen molecules in the large cages have been separated from those in the small cages. A theoretical model, consisting in rigid cages enclosing interacting hydrogen molecules, has been exploited to calculate, on the basis of quantum mechanics, the Raman intensity of the rotational transitions for up to two interacting molecules in one cage. A comparison with experiment leads to a clear interpretation of sidebands appearing in the Raman rotational lines. The quantitative agreement between theory and experiment obtained in some cases clarifies the importance of the choice of the interaction potential, and of the proton disorder in the clathrate crystal.

The vibrational g-factor of dihydrogen from theoretical calculation and analysis of vibration-rotational spectra

We present the first results from quantum-chemical calculation of a vibrational g-factor; the calculations were performed at the level of full configuration interaction using a basis set of aug-cc-pVQZ quality. The theoretical results are consistent with experimental results from analysis of pure rotational and vibration-rotational spectra of dihydrogen in six isotopic variants, in which calculated results for either the rotational g-factor or adiabatic corrections are employed to constrain fits of coefficients of radial functions from wave numbers of transitions. When fits are constrained with data for the rotational g-factor, we reproduce also the radial dependence of adiabatic corrections relative to their value at equilibrium internuclear separation.