Electronic states of HNO + and HON +

Abstract

The three-dimensional CASSCF-MRCI potential energy functions have been calculated for the X 2 A ′ and A 2 A ″ electronic states of the HNO + and HON + isomers. In both cases, these two states form a bent-linear Renner–Teller pair in 2Π symmetry. The barriers to linearity of the X state are calculated to be 6846 cm −1 for HNO + and 8050 cm −1 for HON + (RCCSD(T)). Both isomers possess a conical intersection arising from the crossing between the first excited 2Σ + state and the X 2Π state along the collinear ( NO +( X 1Σ +)+ H( 2 S)) dissociation path. The barrier for isomerisation has been calculated to be 19457 cm −1 (MRCI) and the HNO + isomer is more stable than HON + by 5819 cm −1. The rovibronic levels in the HNO + Renner–Teller system have been calculated by a variational method taking into account the coupling of the rovibrational, electronic and electron spin angular momenta. Since for HON + the barrier to dissociation of the X 2 A ′ ground state is located below the barrier to linearity, only low lying vibrational levels have been calculated for this isomer.