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

Abstract

An analytical expression is found for the accurate ab initiopotential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5cm−1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30cm−1 of the experimental value of 12953±8cm−1. The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation,spin-orbit coupling, and scalar relativity. The Dunham analysis [Phys. Rev.41, 721 (1932)] of the spectrum is found to be very accurate. New values are given for the spectroscopic constants. KeywordsAb initio calculations, Dissociation energies, Polynomials, Dissociation, Electron correlation calculations Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 127 (2007) An analytical expression is found for the accurate ab initio potential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F 2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5 cm −1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30 cm −1 of the experimental value of 12 953± 8 cm −1 . The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation, spin-orbit coupling, and scalar relativity. The Dunham analysis ͓Phys. Rev. 41, 721 ͑1932͔͒ of the spectrum is found to be very accurate. New values are given for the spectroscopic constants.

Active Thermochemical Tables: dissociation energies of several homonuclear first-row diatomics and related thermochemical values

“…The prominent contributors to the provenance are a mix of experiment and theory. They include the experimental ionpair formation threshold by Yang et al [77,78] (with an uncertainty augmented during the ATcT analysis), the bond dissociation determination of Colbourn et al [72], together with the theoretical bond dissociation energies of Bytautas et al [79], Csontos et al [80], Harding et al [4], Karton et al [5], Feller et al [56], as well as a large number of other experimental and theoretical determinations. These include additional species such as ClF, CF 4 , Cl, FOF, HF, HCl, CF, CF 2 , CF 3 , COF 2 , C 2 F 4 , CO 2 , CH 4 , CH, H 2 O, H 2 , and graphite, through alternative thermochemical cycles that ATcT find to be of some relevance to establishing the final result.…”

“…The quoted conclusions of Csontos et al [80] are incorrect; these authors assumed that the ATcT result is derived directly from the value of Colbourn et al [72], while in fact, as we have shown above, the provenance of the ATcT values for D 0 (F 2 ) and D f H°(F) is highly distributed and essentially (in fact, 97 %) independent of the value of Colbourn et al As discussed above, the numerical near-coincidence between the estimate of Colbourn et al and the roughly five times more accurate ATcT value is fortuitous. Furthermore, the possible influence of the dissociation barrier on the ATcT result was checked immediately after the result of Bytautas and Ruedenberg [79] became public. With the possible exception of the estimate of Colbourn et al [72], none of the other *1,200 determinations contributing to the provenance of the thermochemistry of F is affected by the dissociation barrier in the ground state of F 2 .…”

Potential energy curves for Mo2: multi-component symmetry-projected Hartree–Fock and beyond

“…To this end, we use the CEEIS-FCI method [46,47] for generating a set of benchmark results for selected points along the ground-state PEC. The CEEIS-FCI method has been successful in producing high-quality benchmarks for PECs that yielded near-spectroscopic accuracy in the rotational-vibrational spectrum for a number of small molecules [49,51,52]. Furthermore, we shall compare CEEIS-FCI data with the corresponding data generated at the ic-MR-ACPF and ic-MR-AQCC levels of theory that are considered (see, e.g.…”

“…This work also examines the accuracy of three well-established multi-reference methods, namely, complete active space self-consistent field (CASSCF) [42,43], internally contracted multi-reference averaged coupledpair functional (ic-MR-ACPF) [44], and internally contracted multi-reference averaged quadratic coupled-cluster (ic-MR-AQCC) [45], and compare them with the CEEIS-FCI (correlation energy extrapolation by intrinsic scaling) benchmark [46][47][48][49][50][51][52] for selected geometries along the PEC for the molybdenum dimer. We note that the CEEIS-FCI method provides an approximation to the FCI ground-state energy, which constitutes the exact lowest-energy eigenvalue of the Hamiltonian for a given basis set.…”

“…The estimated error bars in CEEIS-FCI energies for systems that are composed of first and second row atoms are typically in the range of 0.2 millihartree (see Refs. [46][47][48][49]) when the reference active space is chosen to include all strongly occupied molecular orbitals.…”