Spectroscopic constants and molecular properties of the X2 Π and a 4 Σ− electronic states of the SiF radical

Abstract

The potential energy curves (PECs) of the X2Π and a4Σ− electronic states of the SiF radical have been studied by an ab initio quantum chemical method. The calculations have been made using the complete active space self-consistent field (CASSCF) method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with several correlation-consistent basis sets. The effects on the PECs by the core-valence correlation and relativistic corrections are included. The way to consider the relativistic correction is to use the third-order Douglas–Kroll Hamiltonian approximation. The relativistic corrections are made at the level of cc-pV5Z basis set. The core-valence correlation corrections are performed using the cc-pCV5Z basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). These PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. Using these PECs, the spectroscopic parameters are determined and compared with those reported in the literature. With these PECs obtained by the MRCI+Q/CV+DK+56 calculations, the vibrational levels, inertial rotation, and centrifugal distortion constants of the first 20 vibrational state of each electronic state are calculated when the rotational quantum number J equals zero. Comparison with the Rydberg-Klein-Rees (RKR) data shows that the present results are reliable and accurate. The molecular constants of the X2Π and a4Σ− electronic states determined by the MRCI+Q/CV+DK+56 calculations should be good prediction for future laboratory experiment. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011