Accurate ab initio potential energy curve of F2. II. Core-valence correlations, relativistic contributions, and long-range interactions

Abstract

The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F2molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spinorbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion. The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F 2 molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spin-orbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion.

Accurate ab initio potential energy curve of F2. I. Nonrelativistic full valence configuration interaction energies using the correlation energy extrapolation by intrinsic scaling method

“…These additional energy terms will be determined and added in the subsequent paper. 145 From the resulting fully ab initio potential energy curve of F 2 , the vibrational and rotational energy levels will then be calculated and compared with the experimentally determined spectrum. 109 The accuracy of CEEIS method can be pushed further by taking into account larger CI expansions.…”

“…143͒; G 0 = experimental zero-point energy 2.075 mhartree ͑from Table X in the third paper of the present series 144 ͒; E CV + E SO + E SR = energy contribution due to corevalence correlations ϩ spin-orbital coupling ϩ scalar relativistic corrections ϭ 1.564 mhartree ͑from Table IV in the second paper in this series 145 ͒.…”

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

“…The vibrational levels they calculated yield errors of ϳ100 cm −1 for v = 19, which is surprisingly close considering the smallness of the basis set and the approximations used. Recent work of Nooijen and Le Roy 53 reports potential energy curves and spectroscopic constants for N 2 and O 2 derived from up to eight low lying vibrational energy levels. Here, as in the work of Laidig et al, 51 the use of the small cc-pVDZ basis stands in the way of a realistic vibrational spectrum.…”

“…The quantum mechanical ab initio calculations in the two preceding papers 1,2 have accounted for all physical interactions that are expected to have a bearing on the potential energy curve for the ground state dissociation of F 2 with an error bar of a few tenths of a millihartree: electronic correlations as well as relativistic effects including spin-orbit coupling. These energies were obtained at 13 internuclear distances along the dissociation curve.…”

“…In the present investigation, we use the potential energy curve determined in the preceding two papers 1,2 to calculate the dissociation energy as well as the full vibration rotation spectrum. The dissociation energy has recently been determined by Yang et al 94 using ion-pair dissociation imaging.…”