Abstract
The potential energy of the molecular ion H₂Cl+ in its three lowest 1A′ states has been calculated over a wide range of the three interatomic coordinates, using MRCI (multi reference configuration interaction) wavefunctions. These potential energy functions (PEF) control the charge transfer reactions between H⁺ and HCl. In particular, the Σ versus Π conical intersection region leading to the H⁺ + HCl (X¹Σ⁺)→H⁺HCl⁺ (X²Πi) reaction (I) and the 21A′ versus 31A′ avoided crossing regi for the reaction H⁺+HCl (X1Σ⁺)→H⁺HCl⁺ (A2Σ⁺) (II) were investigated in detail. It was found that reaction (I) will procee preferentially in collinear and reaction (II) in perpendicular orientations of the proton velocity relative to the HCl molecule axis at low impact energies. Both charge transfer processes occur already at large H⁺-HCl internuclear distances. For reaction (II) the lengthening of the HCl bond leads to a closer approach of the 21A′ and 31A′ PEFs. The quality of the PEFs was tested by a comparison with available spectroscopic data for the electronic ground state of H₂Cl+ near its equilibrium geometry. For instance, the theoretical equilibrium geometry agrees for RCl-H to within 0.0015 \AA, for the angle θH-Cl-H to within 0.4°, and the fundamental vibrational frequencies to within 6-16 cm-1 with available experiments. The first electronically excited state A 1Πu of H₂Cl+ has an attractive potential energy function along the symmetric stretch and bending coordinates, but the antisymmetric stretch cut is repulsive towards the H⁺HCl⁺ (X²Πi) dissociation asymptote. The calculated excitation and asymptotic energies strongly suggest that all higher electronically excited states of H₂Cl+ will be dissociative. ©1991.
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