Ro-vibronic spectrum of the HCSi radical

The three-dimensional potential energy functions for the two components of the X2П ground state of HCSi isomer have been determined by multi-reference contracted CI calculations. These potentials have been used in beyond Born-Oppenheimer variational calculations of the ro-vibronic energy levels including the couplings of rotation-vibration, the electron spin and the electronic angular momenta: band origins are given up to 4000 cm−1. Selected MRCI calculations on the HSiC isomer have shown that the more stable structure of this isomer is a bent 2A′ , stabilized however by a small barrier of only 2800 cm1̄. The geometry of the saddle point between the two isomers has been located.