The ionization potentials of NH2: The multiconfigurational spinhyphen;tensor electron propagator method (MCSTEP) applied to a polyatomic openhyphen;shell radical

摘要

The multiconfigurational spinhyphen;tensor electron propagator method (MCSTEP) gives accurate ionization potentials (IPs) and electron affinities (EAs) for both closedhyphen;shell and openhyphen;shell molecules, including for highly correlated systems. Both principal and lowerhyphen;lying shakeup IPs can be accurately obtained and straightforwardly characterized using MCSTEP. To further test this new technique, we have applied the MCSTEP approach to the openhyphen;shell, polyatomic radical NH2. We report and characterize vertical IPs 0ndash;20 eV, including several ionizations that have not, as yet, been observed experimentally. IPs to both singlet and triplet states of NH+2are accurately calculated using the same MCSCF reference state. We predict the presence of previously undetected, observable vertical PES IPs to states of3A2,1A1, and1A2symmetries at 16.86, 18.00, and 18.26 eV, respectively. Also, we calculate adiabatic IPs by a modified application of the procedure. By examining the two lowest adiabatic IPs with both MCSTEP and Dgr;multireference singles+doubles CI at geometries established by Poplersquo;s research group and with the basis set used by that group augmented by hydrogendpolarization functions we conclude that their MP4 procedures overestimate the IPs with their best basis set by sim;0.2ndash;0.3 eV.