Rydberg States of H4

Abstract

Energies of the 15 lowest Rydberg states of the metastable H4 cluster have been determined using Koopman's theorem at the equilibrium geometry of the parent ion, H4+. To represent the core orbitals of H4, a 6-31G** basis set has been used at the SCF, MP2, MP4(SDTQ), CI-SD, and CI-SDT levels. The Rydberg orbitals have been modeled using a basis set analogous to that used to model the Rydberg orbitals of H3 in previous theoretical calculations. To test the validity of the calculations for the H4 molecule, ab initio calculations were repeated for the Rydberg orbitals of the H3 molecule at the stable geometry of the H3+ core. Predicted transitions were within 2% of the rotational band spectra of H3 observed by Herzberg. The metastable H4 cluster formed from charge neutralization of H4+ decomposes into two H2 molecules. Previous calculations have predicted that one of the two H2 products will be vibrationally hot while the other will be relatively cold and that a large recoil energy of approximately 9 eV is ex...