Ab Initio Study on Spectroscopic Properties of GdF3 and GdCl3

Modelling the matrix shift on the vibrational frequency of ThO by DFT-D3 calculations

Benchmark calculations with a goal to find dispersion-corrected DFT-D3 methods suitable for a reliable estimation of matrix shifts on the vibrational frequency were carried out on the ThO molecule in three rare gas (Rg = Ne, Ar, and Kr) matrices. The matrices were modelled by the explicit approach, in which a single and a double shell of Rg atoms around ThO was considered. The selection of exchange-correlation functionals was based on test calculations on triatomic ThO⋯Rg models. The B3LYP, PBE0, CAM-B3LYP, and LC-ωPBE functionals were found to be the best suited for the estimation of matrix shifts. The single shell of Rg's around ThO accounted for a major part of the shifts; the addition of a second Rg shell resulted only in a minor improvement. Continuum solvation models considerably overestimated the effect of Rg matrices both when the whole matrix was treated by the model and when the first shell was treated explicitly and the rest with a continuum solvation model.

Quasilinear Molecule par Excellence, SrCl2: Structure from High-Temperature Gas-Phase Electron Diffraction and Quantum-Chemical Calculations—Computed Structures of SrCl2⋅Argon Complexes

The molecular geometry of strontium dichloride has been determined by high-temperature electron diffraction (ED) and computational techniques. The computation at the MP2 level of theory yields a shallow bending potential with a barrier of about 0.1 kcal mol(-1) at the linear configuration. The experimentally determined thermal average Sr--Cl bond length, r(g), is 2.625+/-0.010 A and the bond angle, angle-spherical(a), is 142.4+/-4.0 degrees . There is excellent agreement between the equilibrium bond lengths estimated from the experimental data, 2.607+/-0.013 A, and computed at different levels of theory and basis sets, 2.605+/-0.006 A. Based on anharmonic analyses of the symmetric and asymmetric stretching as well as the bending motions of the molecule, we estimated the thermal average structure from the computation for the temperature of the ED experiment. In order to emulate the effect of the matrix environment on the measured vibrational frequencies, a series of complexes with argon atoms, SrCl(2)Ar(n) (n=1-7), with different geometrical arrangements were calculated. The complexes with six or seven argon atoms approximate the interaction best and the computed frequencies of these molecules are closer to the experimental ones than those computed for the free SrCl(2) molecule.

Molecular Structure of Magnesium Dibromide: An Electron Diffraction and Quantum Chemical Study

The molecular structure of magnesium dibromide was investigated by high-level computational techniques and gas-phase electron diffraction. The vapor consisted of about 88% monomeric and 12% dimeric species at the electron diffraction experimental conditions at 1065 K. The geometrical parameters and vibrational characteristics of monomeric, dimeric, and trimeric magnesium dibromide species were determined by computations. Very high level computations with extended basis sets and relativistic pseudopotentials on bromine were needed to reach an agreement between computed and estimated experimental equilibrium geometries for the monomer. For both the dimer and the trimer, different geometrical arrangements were tested. Their ground-state structures have halogen bridges with four-membered ring geometries and D2h and D2d symmetry, respectively. Thermodynamic parameters have also been calculated.

Anharmonic, Temperature, and Matrix Effects on the Molecular Structure and Vibrational Frequencies of Lanthanide Trihalides LnX3 (Ln = La, Lu; X = F, Cl)

MP2 and CCSD(T) ab initio calculations have been carried out to elucidate geometrical structure and vibrational frequencies of representative lanthanide trihalides LnX(3) (Ln = La, Lu; X = F, Cl) explicitly including temperature, anharmonic, inert-gas matrix, and spin-orbit effects. The results have been compared with gas-phase electron diffraction, gas-phase IR measurements, and IR spectra of molecules trapped in inert-gas matrices. On the Born-Oppenheimer surface LaCl(3), LuF(3), and LuCl(3) adopt trigonal planar (D(3)(h)()) geometry while LaF(3) assumes a slightly pyramidal (C(3)(v)()) structure. Because of normal-mode anharmonicities, the resulting thermal average bond angles are considerably lower than the equilibrium ones, while vibrationally averaged bond lengths are predicted to be longer. The inert-gas matrix effects, modeled by the coordination of two inert-gas molecules LnX(3).IG(2) (IG = Ne, Ar, Xe, and N(2)), are substantial and strongly depend on the polarizability of coordinating particles. Coordinating inert-gas units always favor the tendency of LnX(3) molecules to adopt planar structure and induce noticeable frequency shifts.