Ab initio potential energy surfaces for excited electronic states of the molecular ion HCN+

Abstract

Potential energy surfaces for the linear ²Π, 2²Π, òΣ⁺, ²Σ⁺, 3²Σ⁺, 1⁴Π and 1⁴Σ⁺ states and for the bent B²Σ⁺/3²A′ state of HCN⁺ have been calculated by a multi-reference configuration interaction (MRCI) method. The persistence of vibrational structure in the photoelectron spectrum of the state above the experimental dissociation asymptote is interpreted in terms of a local maximum on the potential energy surface with respect to stretching the CH bond. The global minimum for this state has a bent geometry with a bond angle of 129°. This is discussed in terms of an avoided intersection with the A′ component of the 2²Π state for bent geometries. The 3²Σ⁺ surface is quasi-bound and it is suggested that a satellite state at 22.5 eV in the photoelectron spectrum of HCN is the 3²Σ⁺ state. The predissociation of the ²Σ⁺ state is discussed and it is suggested that this may occur via non-adiabatic transitions to the 1⁴Π/1⁴A′ surface.