15min:

HIROYUKI KATSUKI AND TAKAMASA MOMOSE, Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, JAPAN.

It has been shown that high-resolution infrared spectroscopy is applicable to the zero-phonon transitions of rotons and vibrons in solid hydrogen. Because the pure vibrational transitions Q_n(0) [v=n 0, J=0 0] of solid parahydrogen become infrared-active only upon interaction with residual J=1 orthohydrogen, studies of the pure vibrational transitions under high-resolution provide detailed and accurate information on intermolecular interactions between hydrogen molecules. Here, we report the high-resolution absorption spectrum of the first overtone pure vibrational transition Q₂(0) of solid parahydrogen.

The high-resolution spectrum of the Q₂(0) transition at around 8070 cm^-1 was observed using a difference frequency laser system\footnoteT.~Momose, T.~Wakabayashi, and T.~Shida, J.~Opt.~Soc.~Am.~B 13, 1706 (1996).. The spectrum shows a complicated spectral feature compared with that of the Q₃(0) transition\footnoteR.~M.~Dickson, T.~Momose, T.~J.~Byers, and T.~Oka, Phys.~Rev. B 57, 941 (1998).. The v=3 vibrational exciton was found to be well localized on the parahydrogen molecule next to an orthohydrogen. On the other hand, since the vibron hopping matrix element of the v=2 state is comparable to the energy shift due to the existence of orthohydrogen, the observed rich spectral structure can be interpreted as due to the v=2 vibron hopping over a limited number of lattice sites in the crystal. We will discuss the quantitative analysis of the observed spectrum.