Potential energy hypersurfaces of H 4 in the ground and the first two singlet excited electronic states

Abstract

MRD-CI calculations on the first three singlet electronic states of H 4 are presented. These calculations show that the trigonal pyramidal geometry, which has been predicted for the energy minimum in the S 2 state on the basis of the recently proposed Maximum Ionicity of the Excited State (MIES) model, is lower in energy than the corresponding planar structures. The calculated total energies at the optimum trigonal pyramidal geometry are −2.04606, −2.04603 and −2.04601 Hartree for S 0, S 1, and S 2, respectively. The corresponding energies for the kite structure are −2.14608, −2.04523 and −1.98163 Hartree while for an optimum square geometry the total energies are −2.09866, −2.02452 and −2.01822 Hartree for S 0, S 1 and S 2, respectively.