Comprehensive high resolution study of the ^MSiH₄ (M=28, 29, 30) tetradecad stretching bands: Appearance and applications of the isotopic substitution effect in molecules of spherical symmetry

A set of new relations between different spectroscopic parameters of the high symmetry XY4 spherical top molecules is derived on the basis of the general isotopic substitution theory, and a comprehensive high accurate analysis of the five stretching bands (the bands nu(1)+nu(3)(F-2), 2 nu(3)(F-2), 2 nu(3)(E), 2 nu(3)(A(1)), and 2 nu(1)(A(1)); the three latter ones are forbidden in absorption) of the tetradecad of the SiH4 molecule is made. The high resolution spectra of (SiH4)-Si-M(M=28,29,30) in their natural abundance were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at the Technische Universit & auml;t Braunschweig, Germany with an optical resolution of 0.003 cm(-1) and theoretically analyzed (in this case, for the first time both for all five bands of the (SiH4)-Si-29 and (SiH4)-Si-30 species, and for 2 nu(3)(E), 2 nu(1)(A(1)) bands of the (SiH4)-Si-28 one). The number of 2713 transitions of the (SiH4)-Si-28 species (which is more than fourteen times higher compared to analogous studies carried out earlier) belonging to all five ro-vibrational bands of the tetradecad (which are 272, 1897, 15, 369, and 160 transitions of the nu(1)+nu(3)(F-2), 2 nu(1)(A(1)), 2 nu(3)(A(1)), 2 nu(3)(F-2), and 2 nu(3)(E) bands) were assigned with the values of quantum number J(min)/J(max) = 5/22, 1/24, 14/20, 4/24, and 6/23, respectively. The analysis of the obtained experimental data was made on the basis of the Hamiltonian model which takes into account all effects and resonance interactions which are possible in such molecular system. The weighted fit of the 2713 transitions led to a set of 40 rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters which reproduce the initial experimental data with an accuracy of d(rms)=4.11x10(-4) cm(-1). An analogous analysis was made for the two other isotopologues, (SiH4)-Si-29 and (SiH4)-Si-30, of silane. In this case, the initial values of the most important spectroscopic parameters of both species were theoretically estimated on the basis of results of the isotopic substitution theory. As the result of the analysis, two sets of the 12 spectroscopic parameters were obtained from the weighted fits for the (SiH4)-Si-29 and (SiH4)-Si-30 molecules which reproduce the 461 and 375 initial ro-vibrational transitions with the d(rms) of 3.91x10(-4) and 4.9710(-4) cm(-1).