THE IONIZATION-POTENTIALS OF NH2 - THE MULTICONFIGURATIONAL SPIN-TENSOR ELECTRON PROPAGATOR METHOD (MCSTEP) APPLIED TO A POLYATOMIC OPEN-SHELL RADICAL
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The multiconfigurational spin-tensor electron propagator method (MCSTEP) gives accurate ionization potentials (IPs) and electron affinities (EAs) for both closed-shell and open-shell molecules, including for highly correlated systems. Both principal and lower-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 open-shell, polyatomic radical NH2. We report and characterize vertical IPs 0-20 eV, including several ionizations that have not, as yet, been observed experimentally. IPs to both singlet and triplet states of NH2+ are accurately calculated using the same MCSCF reference state. We predict the presence of previously undetected, observable vertical PES IPs to states of 3A2, 1A1, and 1A2 symmetries 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 multireference singles + doubles CI at geometries established by Pople's research group and with the basis set used by that group augmented by hydrogen d polarization functions we conclude that their MP4 procedures overestimate the IPs with their best basis set by 0.2-0.3 eV. 1988 American Institute of Physics.
