Molecular orbital studies of vibrational frequencies

Abstract

Molecular orbital techniques for the ab initio computation of harmonic force constants are reviewed. Extensive applications with the split-valence 3-21G basis are described and a systematic comparison between theoretical and experimental frequencies is undertaken. The 3-21G force constants are permanently stored on a disk file and may be used to predict frequencies for isotopically substituted species. Applications are made to some deuterated molecules.

Global warming potential estimates for the C<sub>1</sub>–C<sub>3</sub> hydrochlorofluorocarbons (HCFCs) included in the Kigali Amendment to the Montreal Protocol

“…It was recognized that computed harmonic frequencies derived via the second derivative of energy as a function of atomic position were systematically higher than observed fundamentals and scale factors were introduced (Hout et al, 1982;Pople et al, 1981). For Hartree-Fock frequencies these were typically ∼ 0.9 and accounted both for the influence of anharmonicity and deficiencies in the underlying quantum calculations.…”

Theoretical determination of the favorable mechanism of the reaction between AlX and HX (X = Br, Cl, and F)

“…The zero-point energy (ZPE) corrections were carried out at the B3LYP/6-311G(d,p) level. The ZPEs were scaled up by the factor 0.9153 [21]. To explicitly establish the relevant species, the intrinsic reaction coordinate (IRC) [22,23] was also calculated for all the transition states that appear on the energy surface profile.…”

A Prebiotic Surface Catalysed Photochemically Activated Synthesis of L-Cysteine

“…The standard calculations at the HF and MP2 levels including zero-point energy corrections [13], together with scaling [14], using the same basis set, 6-31G*, are as previously published [5]. Enthalpy changes at the HF level not including scaled zero point energies are designated as ΔH.…”