Electronic Structure of HCl

An approximate molecular Hartree—Fock electronic wavefunction has been obtained for the ground state of the hydrogen chloride molecule at three closely spaced internuclear distances. This work is of accuracy intermediate between the LCAO approximation and a true molecular Hartree—Fock calculation, since a double orbital basis set is used for the L and M shells of Cl together with extra H orbitals, but 3d basic orbitals are not included. There are 12 basis orbitals of σ symmetry and five of π symmetry. Orbital exponents are determined by variational calculations on atomic chlorine. The computed results include molecular electric dipole and quadrupole moments and their derivatives, estimates of the excitation energy of several low-lying excited states of the neutral molecule and of the positive ion, estimates of the equilibrium internuclear distance of those states that are bound, and identification of the lowest purely repulsive state.