Theoretical Investigations of the Electronic Structure of HeHO⁺and HeHO²⁺

The (3) Sigma(-) and (1)A' of HeHO+ and (2)A" ground electronic states of HeHO2+ have been investigated using the all-electron coupled cluster single, double, and triple-excitation (CCSD(T)) method coupled with an augmented correlation-consistent polarized core valence triple-zeta basis set (aug-cc-pCVTZ). For the (3) Sigma(-) and (1)A' states of HeHO+, the CCSD(T)/aug-cc-pCVTZ model yielded optimized geometrical parameters (r(O-H), r(O-He), theta(H-O-He)) of (1.036 Angstrom, 2.608 Angstrom, 180 degrees) and (1.150 Angstrom, 1.009 Angstrom, 94.7 degrees) respectively, with the triplet state being more stable by 40.4 kcal mol(-1). For the (2)A" ground electronic state of HeHO2+, the optimized structural parameters were (1.247 Angstrom, 1.158 Angstrom, 101.3 degrees) respectively. The calculated harmonic frequencies were real for all these states, and their magnitudes were sensitive to the incorporation of configuration interaction.