Spectroscopy and dynamics of rare gas-spherical top complexes .2. The infrared spectrum of the nu(3) band of Ne-SiH4 (j=1<-0 and j=0<-1 transitions)

The infrared spectrum of the rare gas-spherical top complex Ne-SiH4 has been recorded in a supersonic jet in the region of the SiH4 nu(3) triply degenerate stretching vibration at similar to 2189 cm(-1). In contrast to the previously measured Ar-SiH4 spectrum which showed almost equal rotational spacings within each band (corresponding to transitions between different internal rotor states of SiH4 within the complex), the Ne-SiH4 spectrum is complex with no obvious regular band structure. However, by analogy with the Ar-SiH4 spectrum, four bands of the Ne-SiH4 have been assigned and analyzed in terms of Hamiltonians incorporating Coriolis interaction between the angular momentum of the SiH4 monomer unit and the overall end over end rotation of the complex. These bands correlate with the SiH4 R(0) (K=0<--0, K=1<--0) and P(1) (K=0<--0, K=0<--1) transitions. Derived rotational constants demonstrate that the neon-silane separation (similar to 4.13 Angstrom in the ground vibrational state) is larger than expected by analogy with Ar-SiH4, indicative of nearly free internal rotation by the silane monomer unit in Ne-SiH4. The smaller anisotropy of Ne-SiH4 compared with Ar-SiH4 results in a new angular momentum coupling scheme. Transitions arising from Ne-22-SiH4 correlating to SiH4 R(0) have also been observed and fitted; the higher than anticipated intensities demonstrate a novel isotope enrichment effect in the supersonic jet which is discussed. (C) 1996 American Institute of Physics.