The force constants in the isoelectronic series CF3SO2X (X=F, OH, NH2, CH3): a study based on DFT calculations and experimental data

Density functional theory calculations at the B3LYP/6-31G(d,p) level of theory were performed on the members of the isoelectronic series CF₃SO₂X (X=F, OH, NH₂, CH₃), in order to obtain the optimized geometric parameters and conformations for the four molecules, as well as the wavenumbers corresponding to the normal modes of vibration and the associated force constants. The original force field was transformed to local symmetry coordinates and scaled to reproduce the experimental wavenumbers. The trends observed in geometrical parameters and force constants along the isoelectronic series could be explained making use of the calculated atomic charges.     

The angle deformation force field for the hydrogen-bonded heterodimer CH3CN⋯HF determined with the aid of the centrifugal distortion constant DJK

The relationships between the valence force field and the centrifugal distortion constants are established for a molecule of the general type XY₃WZ?AB and are used in the case of CH₃CN?HF to determine the angle deformation force field by employing D_JK in combination with the wavenumbers of the appropriate vibrational modes.     

Vibrational spectra,force constants and thermodynamic functions of cycloheptasulfur,S71

Raman and IR spectra of four allotropes of cycloheptasulfur are reported. All 15 fundamental vibrations of the S₇ molecule have been observed and were assigned in accordance with the molecular point group C_s. A normal-coordinate analysis using an extended Urey—Bradley force field with 10 independent force constants resulted in very good agreement between observed and calculated wavenumbers. Entropy, heat capacity and other functions of gaseous S₇ have been calculated by statistical methods and evidence for pseudorotation of S₇ in the vapor state is presented. The molecular structure as well as the valence force constants of S₇ are rationalized by a qualitative molecular orbital treatment.     

Normal coordinate analysis of CF3CH3

Normal coordinate calculations were made for CF₃CH₃, using a twenty-two parameter modified valence force field. Thirteen force constants were constrained to the CF₃CH₂X values and nine were adjusted to fit the twelve frequencies, resulting in an average error of 2.3 cm^/t-1. The CF₃ group force constants should be useful in calculations for other compounds containing this group.     

Force constants,coriolis coupling constants and mean amplitudes of vibration of GaF63− and FeF63−

The force constants, Coriolis coupling constants and mean amplitudes of vibration at 0, 298.16 and 500 K for GaF₆^3?FeF₆^3? have been reported for the first time employing recent vibrational data. The results are discussed in the light of available information.     

Force-constant calculations for Ni(PF3)4, Pd(PF3)4 and Pt(PF3)4

Force constants for a SVFF approximation have been obtained for the compounds Ni(PF₃)₄, Pd(PF₃)₄ and Pt(PF₃)₄ using the FG matrix method and vibrational assignments (A₁, E and F₂ symmetry species) on the basis of regular tetrahedral symmetry, point group T_d. Six primary force constants involving bond stretching and bond angle changes and five interaction force constants were used to simultaneously fit the observed wavenumbers. The PF stretching force constant differs by only ± 3% for all three compounds and for the free ligand, PF₃. The metal—phosphorus stretching force constant, however, increases significantly in the order Ni < Pd < Pt, and is 65% larger for Pt(PF₃)₄ than for Ni(PF₃)₄. These changes are discussed in terms of the metal—phosphorus—fluorine bonding in M(PF₃)₄ compounds.     

Korrelation zwischen Bindungsl?ngen und -winkeln, Valenz-Kraftkonstanten und NMR-Kopplungen in Se2Sn3Me6 und Se3Sn3Me6

Ohne Zusammenfassung

---

Correlations between bond lengths and angles, force constants and NMR coupling in Se₂Sn₃Me₆ and Se₃Sn₃Me₆

     

Scaled Quantum Mechanical Force Fields for the CF3SX Molecules (X = H,F, Cl,Br, I)

Density functional theory calculations at different levels of theory were performed on the molecules of the series CF₃SX (X = H, F, Cl, Br, I) in order to obtain their optimized geometric parameters and conformations, the wavenumbers corresponding to the normal modes of vibrations and the associated force constants. The obtained force fields were transformed to local symmetry coordinates and scaled to reproduce the experimental wavenumbers.     

Solution raman spectra and normal coordinate analysis of the H3CPH+3 and H3CPD+3 cations

The Raman spectra of solutions of H₃ CPH₃⁺ and H₃ CPD₃⁺ in aqueous concentrated hydrochloric and deuterochloric acid are reported together with polarisation data. A complete vibrational assignment is given on the basis of C_3v, symmetry except for the inactive A₂ mode. A set of valence force constants and potential energy distributions have been calculated from the data of the two isotopes H₃ CPH₃ and H₃⁺ CPD⁺₃. For H₃ CPD⁺₃ the potential energy distribution demonstrates strong interaction between the P-C stretching and the symmetrical PD₃ deformation mode.     

Molecular vibrational constants of some simple polyatomic molecules: trihalogenomethanes,CHX3 and trihalogenosilanes,SiHX3 (X = F,Cl, Br)

Force constants and compliance constants for the CHX₃ and SiHX₃ molecules have been obtained, using the vibrational frequencies of CHX₃ and CDX₃ (SiHX₃ and SiDX₃) molecules only. The reliability of the resulting force field has been checked by calculation of Coriolis coupling constants, centrifugal distortion constants and mean amplitudes of vibration and by comparison with the available experimental data.     

The harmonic force fields of BF3, SnCl4 SbBr3 obtained by the joint use of electron diffraction and vibrational spectroscopy data

The recently developed technique of joint analysis using electron diffraction and vibrational spectroscopy data for determining molecular force fields is demonstrated for the sample molecules BF₃ and SnCl₄. The technique is based on harmonic force constants being the common parameters in the interpretational methods of both components. The general harmonic force field of SbBr₃ is refined in this way using electron diffraction and recently available gas-phase spectroscopic frequencies of vibration.     

Investigation of Raman and infrared phonon modes in case of barium bismuth tantalate (BaBi2Ta2O9)

The Raman and the infrared wavenumbers in the Aurivillius structure BaBi₂Ta₂O₉ (BBT) having space group I4/mmm (no. 139-D_4h¹⁷) are investigated using normal coordinate analysis. The calculation of zone center phonons incorporates seven stretching and seven bending force constants. The Raman and the infrared frequencies for BBT have been assigned for the first time in I4/mmm phase. The calculated Raman and infrared wavenumbers are in very good agreement with the observed ones. The potential energy distributions (PED) are also investigated for each normal mode in BBT and the contributions of different force constants to various frequencies are determined.     

Partial reassignment of the fundamental modes of As(CCH)3 and Sb(CCH)3; valence force constants and mean amplitudes of vibration for As(CCH)3

The vibrational frequency assignments for As(CCH)₃ and Sb(CCH)₃ reported by Miller and Lemmoa are discussed. Partial reassignments are proposed based on simple and advanced force field calculations. For the As-compound, valence force constants and mean amplitudes of vibration have been calculated and compared with those of related compounds. Evidence is found for some d-orbital participation in the As-C bond.     

Vibrational spectra,normal coordinate analysis and mean amplitudes of methyl borate,B(OCH3)3

Infrared spectra for methyl borate, B(OCH₃)₃ were recorded in the gas phase and solutions. Raman spectra were recorded for the same compound in liquid and solid states. The data were interpreted on the basis of a C_3h molecular model. A normal coordinate analysis for the complete model is included. The developed force constants were used to calculate the mean amplitudes of vibration which were compared with recent results from electron diffraction.     

Isotopic invariants of pyramidal symmetrical XY3 molecules and evaluation of molecular constants

The isotopic invariants of pyramidal symmetrical XY₃ molecules are calculated in terms of frequencies, Coriolis coupling constants, molecular geometry parameters and masses of the constituent atoms. These invariants are used to evaluate force constants, compliance constants and mean amplitudes of vibration of four sets of 12 isotopic molecules.     

On the geometry and internal rotation of XSCF3 compounds (X = F,Cl and CF3)

The molecular structures (r_α⁰ values) for XSCF₃ with X = F, Cl and CF₃ have been determined by electron diffraction of gases. While the geometry (C-F bond length and FCF angle) of the CF₃ groups and the bond angle at the sulfur atom depend very little on the substituent X, the S-C bond length increases with decreasing electronegativity of X from 1.805 (3) Å for X = F to 1.824 (6) Å for X = Cl. Torsional force constants for the CF₃ groups were derived from vibrational amplitudes. A strong increase of this force constant is observed between FSCF₃ (f_τ = 0.09 (2) mdyn Å) and CISCF₃ (f_τ = 0.18 (5) mdyn Å). The torsional frequencies derived from the electron diffraction experiment agree very well with the values observed in the far IR spectra for CISCF₃, and CF₃SCF₃. A force field for CF₃SCF₃ has been derived from IR and Raman data.     

Schwingungsspektren und normalkoordinatenanalyse von CF3,-verbindungen : XXVI. Molekülstrukturen und schwingungsspektren von α-CF3HgN3 und CF3HgNCO

The crystal structures of the isostructural compounds α-CF₃HgN₃ (I) and CF₃HgNCO (II) were determined by X-ray methods. Centrosymmetric dimers are formed with weak Hg---n′ bonds of 2.74(2) Å in I and 2.88(2) Å in II. The Hg---N distance and Hg---N---N angle are 2.02(2) Å and 127(2)° in the monomeric fragment of I, the corresponding values in II are 2.03(2) Å and 137(2)°. Raman and, in part, IR spectra of both compounds in the solid state were recorded and assigned for Cs and C_2h symmetry of the monomers and dimers, respectively. A normal coordinate analysis proved that the stretching vibrations of the (HgN)₂ four-membered ring appeared at ≈400 and ≈75 cm^-1; the force constants amounted to ≈2.0 for the short and to ≈0.25 X 10² N/m for the long HgN bonds.     

Superparameterization of low-temperature vibrational data for lanthanide hexahalide anions

A complete dataset is presented for the modes of vibration of LnCl³⁻₆ in Cs₂NaLnCl₆, from low temperature Raman and vibronic spectroscopy. Conventional force constant calculations with this dataset are unsatisfactory since, although the datafits are quite good, the physical significance of the derived force constant parameters is not clear in all cases. A parameterization of 30 vibrational wavenumbers at a time, comprising five datasets of six modes of vibration, enables the relative importance of the GVFF interaction force constants to be ascertained. The trans stretch—stretch force constant is about 2.5 times larger than the cis interaction constant, and the angle—angle interaction constants all have comparable magnitudes. However, the same ratios for the magnitudes of the interaction force constants fail to provide a satisfactory datafit for PrBr³⁻₆ in Cs₂NaPrBr₆. This is attributed to the stronger trans directing influence of the bromide ligand than the chloride ligand, and an increased ratio for the trans/cis stretching interaction force constant provides a more satisfactory fit. Datasets are also presented for LnF³⁻₆ and Cs₂LiLnCl₆. The nature of the cation A in Cs₂ALnCl₆ appreciably modifies the moiety mode vibrational wavenumbers.     

Vibrational spectroscopic investigations of snse8-n molecules

The fundamental vibrations of 13 cyclic S_nSe_8-n (n = 7—2) molecules have been calculated using a modified Urey—Bradley force field with 9–14 independent force constants whose values have been adapted from those of Se₈ and S₈. Calculated wavenumbers are compared to those obtained by Raman spectroscopy for sulfur—selenium phases prepared by recrystallizing quenched molten mixtures of the elements as previously described. Agreement between the observed spectra and calculated wavenumbers is closest by assuming the existence of selenium—selenium bonds and the absence of isolated selenium atoms in S_nSe_8-n molecules. It is assumed that sulfur—selenium phases are mixed crystals with the following components in varying concentrations: 1,2-S₆Se₂, 1,2,3-S₅Se₃, 1,2,3,4-S₄Se₄, 1,2,5,6-S₄Se₄, 1,2,3-S₃Se₅ and 1,2-S₂Se₆. The presence of S₈ and Se₈ in some of the phases is indicated by the Raman spectra.     

On the nonstatistical character of chemically activated CHF2Cl* and CHF3* decomposition

The RRKM theory and the quantum variation of RRK theory are used to calculate the decomposition rate constants of chemically activated CHF₂Cl^* and CHF₃^*. The calculated values of the rate constants are compared with experimental data. It is shown that the decompositions of CHF₃^* and CHF₂Cl^* proceed much faster than they should in terms of statistical theory.