Ab initio potential energy surfaces for excited electronic states of the molecular ion HCN+.
Potential energy surfaces for the linear X2Pi, 2(2)Pi, A2Sigma+ , B2Sigma+, 3(2)Sigma+, 1(4)Pi and 1(4)Sigma+ states and for the bent B2Sigma+/3(2)A' 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 B 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 degrees. This is discussed in terms of an avoided intersection with the A' component of the 2(2)Pi state for bent geometries. The 3(2)Sigma+ surface is quasi-bound and it is suggested that a satellite state at 22.5 eV in the photoelectron spectrum of HCN is the 3(2)Sigma+ state. The predissociation of the B2Sigma+ state is discussed and it is suggested that this may occur via non-adiabatic transitions to the 1(4)Pi/1(4)A' surface.
Hirst
David M
DM
Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL.