Anharmonic vibrational frequencies and vibrationally averaged structures and nuclear magnetic resonance parameters of FHF−

Abstract

The anharmonic vibrational frequencies of FHF(-) were computed by the vibrational self-consistent-field, configuration-interaction, and second-order perturbation methods with a multiresolution composite potential energy surface generated by the electronic coupled-cluster method with various basis sets. Anharmonic vibrational averaging was performed for the bond length and nuclear magnetic resonance indirect spin-spin coupling constants, where the latter computed by the equation-of-motion coupled-cluster method. The calculations placed the vibrational frequencies at 580 (nu(1)), 1292 (nu(2)), 1313 (nu(3)), 1837 (nu(1) + nu(3)), and 1864 cm(-1) (nu(1) + nu(2)), the zero-point H-F bond length (r(0)) at 1.1539 A, the zero-point one-bond spin-spin coupling constant [(1)J(0)(HF)] at 124 Hz, and the bond dissociation energy (D(0)) at 43.3 kcal/mol. They agreed excellently with the corresponding experimental values: nu(1) = 583 cm(-1), nu(2) = 1286 cm(-1), nu(3) = 1331 cm(-1), nu(1) + nu(3) = 1849 cm(-1), nu(1) + nu(2) = 1858 cm(-1), r(0) = 1.1522 A, (1)J(0)(HF) = 124+/-3 Hz, and D(0) = 44.4+/-1.6 kcal/mol. The vibrationally averaged bond lengths matched closely the experimental values of five excited vibrational states, furnishing a highly dependable basis for correct band assignments. An adiabatic separation of high- (nu(3)) and low-frequency (nu(1)) stretching modes was examined and found to explain semiquantitatively the appearance of a nu(1) progression on nu(3). Our calculations predicted a value of 186 Hz for experimentally inaccessible (2)J(0)(FF).

Symmetry and dynamics of FHF− anion in vacuum, in CD2Cl2 and in CCl4. Ab initio MD study of fluctuating solvent–solute hydrogen and halogen bonds

“…44 The NMR parameters of FHF À anion have been computed by several authors. 35,41,45 The results show the low-field bridging proton chemical shift and high values of the 1 J HF and 2h J FF coupling constants for the isolated anion, which reproduce rather well the available experimental data. Additionally, in ref.…”

“…In some cases computed frequencies match rather well -difference less than 10 cm À1 -with the experiment. [39][40][41][42] Upon increase of the FÁ Á ÁF distance a barrier for the proton motion appears and grows, eventually rising above the zero-point energy level and creating a dual maximum shape of the proton wave function. 43 It could be argued that in a condensed medium such double well potential is realized along the proton transfer coordinate that includes the solvent molecule motions.…”

Anharmonic vibrational frequencies and vibrationally-averaged structures of key species in hydrocarbon combustion: HCO+, HCO, HNO, HOO, HOO–, CH3 +, and CH3

“…Some of these works are based on QFF in tailored coordinates, vibrational perturbation theories including Coriolis coupling, and various CBS extrapolations of electronic energies, including small electronic effects such as core correlation and relativistic effects as well as diagonal Born-Oppenheimer corrections. In contrast to these previous high-accuracy studies, this study and a few previous ones [5][6][7] from our group aim at establishing blackbox computational procedures for low-lying anharmonic vibrational frequency calculations applicable generally and unambiguously to various polyatomic molecules in the same sense of 'model chemistry' advocated by Pople (see, e.g., [45]) in electronic structure theory. The reliance on normal modes, the mixed use of QFF, grid, and hybrid QFF/grid PES representations, and the open-ended combinations of systematic electronic and vibrational many-body methods in this work are to achieve good balance between general applicability of the theories, robustness and availability of the implementations, and high (if not the highest) accuracy.…”

“…Combined with systematic basis sets such as the ones developed by Dunning and co-workers [3,4], they can now routinely predict the electronic properties of small but general polyatomic molecules within controlled accuracy. The objective of this study as well as several recent ones in our group [5][6][7] is to extend the domain of predictive computing to bound nuclear motions, i.e. anharmonic molecular vibrations, vibrationallyaveraged properties, and various molecular spectra.…”

Solving the vibrational Schrödinger equation on an arbitrary multidimensional potential energy surface by the finite element method

“…The bending mode, however, exhibits virtually no deviation from harmonicity. Most recently, this system has been treated using Fourier grid [81] and vibrational self-consistent field (VSCF) calculations [82] to obtain results that agree with experiment to high precision. Table 1 of Ref.…”