ANHARMONIC CONSTANTS OF SIHCL3 AND CHCL3

Most of the anharmonic constants of trichlorosilane and -methane have been determined, with special emphasis to the values of x(1i), i = 1 to 6. In both molecules, there is a strong Fermi resonance between hydrogen stretch and bend vibrations and Coriolis interaction between nu(2) and nu(5). Some irregularities in the hot band structures point to an interaction of nu(1) with nu(2)+2 nu(4) and other higher order interactions. In SiHCl3, x(13) and x(16) are near 0, in agreement with a rule that nondiagonal anharmonicities between high- and low-frequency vibrations tend to be small. In CHCl3, the corresponding values are larger, though still small. We discuss a possible correlation of such values with the frequency change of one of the vibrations, if the bond corresponding to the other one is dissociated. Ni(CO)(4) is quoted as a further example. The data set could help in calculations of vibrational relaxation rates.