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The 3 and 4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The 4 band shows extremely sharp lines of a width of ϳ0.003 cm Ϫ1 , while the 3 band exhibits broader lines of a width of 1 cm Ϫ1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.

e.g., molecules of biochemical interest, in cooperation with Professor A. A. Bothner-By (Pittsburgh). Attention is also being paid to small molecules to study the correspondence with determinations using microwave spectroscopy.42EFNMR studies are at the moment focused on binary mixtures. The addition of a second component to the solution affects the alignment which thus provides information about intermolecular interactions.43,44 In a recent study,44 the change of the alignment upon dilution is interpreted in possible changes of the quadrupole (42)