15min:

Y. KAWASHIMA, Department of Applied Chemistry, Kanagawa Institute of Technology, Atsugi, Kanagawa 243-03, Japan; R. D. SUENRAM, Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899; E. HIROTA, The Graduate University of Advanced Studies, Hayama, Kanagawa 240-01, Japan.

The microwave spectra of the normal species, ²⁹Si, ³⁰Si, ¹⁸O, and ²H SiH₄--H₂O have been measured using a pulsed-nozzle Fourier transform microwave (FTMW) spectrometer. Two, four and five strong transitions were observed for the J = 1 <- 0, 2 <- 1, and 3 <- 2 transitions, respectively in the 7 to 22 GHz region. Almost all of the observed lines consisted of two or three components. The spectral patterns observed for SiH₄--H₂O were different from those of CH₄--H₂O, CH₄--HCl, and Ar--SiH₄. The observed line frequencies were fitted to the expression for the rotational spectrum of a linear molecule. The centrifugal distortion constant of the set appearing at lower frequencies than the K=0 transition is much smaller than those of other transitions. The rotational constants thus obtained, give an Si-O bond length of 3.38Å, which is much shorter than the C-O bond length in CH₄--H₂O (3.70Å). The value of the stretching force constant estimated for SiH₄--H₂O from the rotational and centrifugal distortion constants is larger than that for the C-O bond in CH₄--H₂O. We thus conclude that the Si-O bond in SiH₄--H₂O is much stronger than the C-O bond in CH₄--H₂O. From the observed Stark effect in SiH₄--H₂O, the electric dipole moment was determined to be 1.730 Debye. The structural and dipole data indicates that the water moiety is located with its C₂ axis coinciding with the van der Waals bond.