Laser spectroscopic studies of the pure rotational &,(O) and l&(O) transitions of solid parahydrogen

High resolution spectrum of multipole-induced transitions of solid parahydrogen was recorded using diode and difference frequency laser spectroscopy. The J = 4 + 0 pure rotational UO( 0) transition observed in the diode spectrum agrees well in frequency with the value reported by Balasubramanian et al. [ Phys. Rev. Lett. 47, 1277 ( 1981) ] but we observed a spectral width smaller by about a factor of 4. The J = 6 c 0 W, (0) transition was observed to be exceedingly sharp, with a width of 70 MHz, using a difference frequency spectrometer with tone-burst modulation. This transition is composed of three components with varying relative intensity depending upon the direction of polarization of laser radiation. These components were interpreted as the splitting of the M levels in the J = 6 state due to crystal field interactions. In addition, a new broad feature was found at 2452.4 cm ’ in the low resolution Fouriertransform infrared (FTIR) spectrum of solid hydrogen and was assigned to be the phonon branch W, (0) transition of the W, (0) line. The selection rules, crystal field splitting of J = 4 and J = 6 rotons, and the measured linewidth based on these observations are discussed.