Ab initio investigations of the electronic structure of HeNH+ and HeNH2+

The 1 A′ and 3 A″ electronic states of HeCH + and the 2 A′ ground electronic state of HeCH 2+ have been investigated using an all electron coupled cluster single, double and triple excitation [CCSD(T)] method coupled with an augmented correlation-consistent polarised core valence triple zeta basis set (aug-cc-pCVTZ). For the 1 A′ and 3 A″ electronic states of HeCH + , the CCSD(T)a aug-cc-pCVTZ model yielded an optimised geometry of C s symmetry eith a { r CHe , r CH , θ HCHe } structural parameters of {2.172 Å, 1.129 Å, 81.4°} and {1.675 Å, 1.121 Å, 101.4°} respectively. Moreover, this electronic model yielded the singlet state to be 26.3 kcal mol −1 lower in energy in energy when compared with the triplet state. For the 2 A′ ground electronic state of HeCH 2+ the optimised structural parameters were {1.388 Å, 1.253 Å, 110.5°}, respectively. The calculated harmonic frequencies for all these electronic states were found to be real.