The (n00), n=3, 4, and 6, local mode states of H3SiD: Fourier transform infrared and laser photoacoustic spectra and ab initio calculations of spectroscopic parameters

The rotational structure of the local mode Si-H stretching vibrational band s (n00 A(1)/E), n = 3, 4, and 6, of (H3SiD)-Si-28 have been studied by high -resolution Fourier transform infrared and by photoacoustic laser spectrosc opy. The recorded bands have been rotationally analyzed with a Hamiltonian model which makes use of simple arithmetic relations between some of the ro vibrational parameters. While the (300 A(1)/E) states were found to be unpe rturbed, severe perturbations by unknown dark states affect the (400 A(1)/E ) and (600 A(1)/E) states for J values exceeding 8. Ab initio calculations have been performed to form the quadratic and the cubic potential energy su rfaces which have been used to calculate spectroscopic parameters for the S i-H stretching fundamentals. These results, together with the local mode re lations, have been successfully used to model the vibrational dependence of effective rovibrational parameters in the excited local mode states. (C) 2 001 American Institute of Physics.