Configuration-Interaction Study of the Ground State of the H3+ Molecule

Abstract

A configuration-interaction calculation on the ground state of H3+ has been done using Slater-type orbitals of the form 1s, 2s, 2px, 2py, 2pz to form the basis set. The calculation was effected by approximating the exact wavefunction for the system by a linear combination of configurations, each of which is a properly antisymmetrized function constructed from the basis orbitals, and by applying the variation theorem to the approximate wavefunction. The most stable nuclear geometry for H3+ is an equilateral triangle, since a plot of total energy versus central bond angle shows a deep minimum at a bond angle of 60 deg. The best energy that was obtained for the equilateral triangle was —1.33264 hartree at R=1.6575 bohr, using 12 basis orbitals and 12 symmetry-adapted configurations. The experimental energy for H3+ is not known, but is estimated to be —1.35 hartree from these calculations. The first excited singlet state, which is a doubly degenerate 1E′ state, has been examined at many values of R for an equilateral triangle with three basis orbitals, and has been found to give a typical repulsive energy curve. The fundamental vibrational frequencies for the ground state have been calculated, and it has been found that the symmetric stretch frequency is 3354±60 cm—1, and the doubly degenerate bending frequency is 2790±100 cm—1.