The weakly bound complex CH4-H-2: Observation and analysis of infrared spectra in the 350 and 1311 cm(-1) regions

Infrared spectra of the weakly bound van der Waals complex CH4-paraH(2) hav e been observed and analyzed for the first time. Measurements were made usi ng a long-path (160-180 m) low-temperature (61-92 K) absorption cell which was probed with a Fourier transform spectrometer and a tunable diode laser. The partly resolved spectrum accompanying the S-0(0) pure rotational trans ition of H-2 around 350 cm(-1) was analyzed in terms of an approximate mode l to obtain the rotational and centrifugal distortion constants of the comp lex in its ground state. The high resolution spectrum accompanying the R(0) transition of the nu(4) fundamental band of CH4 near 1311 cm(-1) was assig ned in detail and analyzed using the Coriolis model used previously for ana logous spectra of methane-rare gas complexes. The effective intermolecular separation and dissociation energy of the complex in its ground state were determined to be about 4.12 Angstrom and 28 cm(-1), respectively. (c) 1999 American Institute of Physics. [S0021-9606(99)00220-2].