SiH2, a critical study

The first four spectroscopic states of the silylene molecule SiH2, namely, (X) over tilde (1)A(1), (a) over tilde B-3(1), (A) over tilde B-1(1) and (B) over tilde (1)A(1) were examined theoretically using multireference methods coupled with very large correlation consistent basis sets. Our aim is understanding why SiH2 has a singlet ground state ((X) over tilde (1)A(1)) as opposed to the (X) over tilde B-3(1) state of the isovalent carbene CH2, as well as the rationalization of its geometric and bonding characteristics. The interpretational philosophy followed is based on strictly calculable quantities in an effort to reduce to a minimum the always present but not well-defined 'chemical intuitionism'. All of our calculated quantities are in excellent agreement with existing experimental results.