Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution

Abstract

The effects of a dielectric medium on the magnetizabilities and nuclear shielding constants of the fluoromethanes are calculated in a gauge-origin independent approach. It is shown that in order to model the effects of a dielectric medium properly, we have to go beyond the dipole approximation and the geometry has to be optimized for each value of the dielectric constant. Geometrical distortions play an important role, as is clearly demonstrated for the magnetizability of the CH 3 F molecule where the geometrical distortions alter the sign of the dielectric contribution to the solvent shift. The effects on the nuclear shielding constants from a dielectric medium are interpreted in terms of the polarization of the charge distribution and the change in geometry. Other medium effects on nuclear shielding constants are discussed, and it is demonstrated that they must be included in order to reproduce the experimental gas-to-liquid chemical shift of the CH 3 F and CHF 3 molecules. Basis set convergence and electron correlation effects of the magnetizabilities and the nuclear shielding constants in the gas phase are also investigated.

Solvent effects on the NMR parameters of H2S and HCN

“…As in our previous studies of solvent effects on the nuclear shieldings, 2,6 we observe that the shielding constant of the most electronegative atom Ž . in a compound increases diamagnetic shift with increasing dielectric constant, whereas the con-Ž stants of the other atoms decrease paramagnetic .…”

“…In this investigation, we have focussed on the latter term to understand E how the dielectric medium induces changes in the magnetic properties of the solvated molecules. In a recent study on the magnetic properties of fluromethanes, 6 we have shown that it is necessary to include all four terms to reproduce the experimentally observed shifts.…”

“…sistent field SCF wave functions. The only exceptions are the investigations of fluoromethanes 6 and hydrogen selenide, 3 both of which used multiconfigurational SCF wave functions. We also mention the combined molecular dynamicsrdensity-functional theory study of liquid water by Malkin et al, 7 the combined molecular dynamicsrab initio 8 approach by Nymand, Astrand, and Mikkelsen of liquid water, and the study of solvent effects on the nuclear shieldings and spin᎐spin couplings of the acetylene molecule by Pecul and Sadlej.…”

The Rotational g Tensor as a Benchmark for Ab Initio Molecular Property Calculations

“…The errors introduced due to truncations in the one-and N-electron spaces (basis set and electron correlation treatment, respectively) are often much larger than the experimental standard deviations obtained in highly accurate molecular beam (MB) [1] and microwave (MW) Zeeman experiments [2]. Theoretical studies of the rotational g tensor have been presented at various levels of theory, including Hartree-Fock [3][4][5], second-order Møller-Plesset perturbation theory (MP2) [6][7][8], the linearized coupled-cluster doubles (L-CCD) method [8], second-order polarization propagator approximation (SOPPA) [9][10][11], multiconfigurational self-consistent-field (MCSCF) theory [12][13][14] and even full configurationinteraction (FCI) [15,16] for diatomic and small polyatomic molecules. The results presented in these studies are in qualitative agreement with experiment but often differ by more than ten experimental standard deviations from experimental measurements, especially at lower levels of theory.…”

Stability and magnetic properties of Co2Om(m= 1,...,7) clusters

“…This basis set has been obtained by optimizing the exponents and contraction coefficients in ground state Restricted Open Hartree-Fock (ROHF) calculations and there are in total 241 contracted functions. It is shown that the isotropic magnetizability and its anisotropy are remarkably constant with respect to the basis set and close to experiment, too [13]. So, the obtained performances allow us to foresee how magnetic properties of the particles depend on their structures.…”