Explicitly correlated treatment of H2NSi and H2SiN radicals: Electronic structure calculations and rovibrational spectra

Various ab initio methods are used to compute the six dimensional potential energy surfaces (6D-PESs) of the ground states of the H2NSi and H2SiN radicals. They include standard coupled cluster (RCCSD(T)) techniques and the newly developed explicitly correlated RCCSD(T)-F12 methods. For H2NSi, the explicitly correlated techniques are viewed to provide data as accurate as the standard coupled cluster techniques, whereas small differences are noticed for H2SiN. These PESs are found to be very flat along the out-of-plane and some in-plane bending coordinates. Then, the analytic representations of these PESs are used to solve the nuclear motions by standard perturbation theory and variational calculations. For both isomers, a set of accurate spectroscopic parameters and the vibrational spectrum up to 4000 cm(-1) are predicted. In particular, the analysis of our results shows the occurrence of anharmonic resonances for H2SiN even at low energies. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624563]