Simple Valence Force Field Research Articles

Normalscliwingungen von Alkalifeldspäten

Abstract The normal modes of vibration of various alkali feldspars were calculated on the basis of a simple harmonic valence force field. Infrared and Raman spectra were recorded over the whole frequency range. With 7 force constants for ordered feldspars and 5 constants for disordered feldspars the calculated frequencies could be fitted with an average deviation of 10–16 cm−1, depending on the compound. The fitting was done by a least-squares method. The model used cannot explain the frequency shifts which are observed in going from an ordered to a disordered Si/Al distribution.

Normal coordinate analysis of potassium and rubidium fluoaluminates

Infrared absorption spectra of alkali fluoaluminate crystals MAlF4 (M: K and Rb) have been measured in the frequency region from 4000–30 cm−1. Both the intramolecular vibrations such as the Al–F bond stretching and the F–Al–F bending vibrations and the lattice vibrations due to the interaction between the inner complex and the outer ions have been observed in the frequency regions of 800–160 cm−1 and below 160 cm−1, respectively. A normal coordinate analysis of the crystal as a whole has been carried out on the basis of a simple valence force field. The force constants of the Al–F stretching, F–Al–F bending, and M · · · F interaction have been obtained and discussed in relation to the interatomic distances. It has also been found that the simple valence force field assumed here is adequate for these complex fluorides.

Molecular orbital studies of interaction force constants in dicarbonyl compounds

Molecular orbital calculations are used to evaluate interaction force constants in biacetyl, acetic anhydride and acetyl acetone. Normal coordinate analyses are performed for these three molecules utilizing the MO-calculated interaction force constants. Analogous normal coordinate calculations are also carried out within the framework of the simple valence force field, in which all interaction force constants are neglected. It is shown that the former calculations reproduce the experimental carbonyl spacings satisfactorily; whereas the latter (SVFF) calculations are grossly in error.

ChemInform Abstract: SINGLE CRYSTAL VIBRATIONAL SPECTRA OF CHLORANIL (2,3,5,6‐TETRACHLORO‐P‐BENZOQUINONE)

The polarized vibrational spectra of single crystals of chloranil are investigated for the first time over the complete energy range of intramolecular and lattice fundamentals. The polarized infra-red spectra of the (001) crystal plane and the a(––)c* set of polarized Raman spectra are presented. The particularly favourable orientation of the molecule inside the crystal and the applicability of the oriented gas model lead to an unusually complete and reliable assignment of the intramolecular fundamentals. A simplified Valence Force Field is used to reproduce the in-plane and out-of-plane vibrational motions.The translational and librational lattice modes are discussed and an almost complete assignment is achieved.

Geometrical Structures of Excited States of Conjugated Molecules. II. The Calculated Vibronic Intensity Distributions in the Absorption Spectra of Naphthalene

Abstract The normal coordinates and the vibrational frequencies in the first excited singlet (1B2u), the second excited singlet (3B1u), and the first excited triplet (3B1u) states of naphthalene, whose geometries were calculated by a semiempirical method, are evaluated by assuming a simplified valence force field. The relation between the normal coordinates of two different electronic states is expressed on the basis of the Franck-Condon principle. The mixing among the excited-state normal coordinates, expressed in terms of the ground-state normal coordinates, is neglected in the present treatment. By using the simple relation between the normal coordinates of two different electronic states, the vibronic intensity distributions in the absorption spectra (1B2u←1Ag, 1Lb, 1B1u←1Ag, 3La, and 3B1u←1Ag,3La) have been calculated. The vibronic intensity distribution of the 1B2u←1Ag transition has been calculated, taking into consideration the intensity of the interpenetrating sets of the vibronic band groups on the basis of the Herzberg-Teller perturbation theory.

Single crystal vibrational spectra of chloranil (2, 3, 5, 6-tetrachloro-p-benzoquinone)

The polarized vibrational spectra of single crystals of chloranil are investigated for the first time over the complete energy range of intramolecular and lattice fundamentals. The polarized infra-red spectra of the (001) crystal plane and the a(––)c* set of polarized Raman spectra are presented. The particularly favourable orientation of the molecule inside the crystal and the applicability of the oriented gas model lead to an unusually complete and reliable assignment of the intramolecular fundamentals. A simplified Valence Force Field is used to reproduce the in-plane and out-of-plane vibrational motions.The translational and librational lattice modes are discussed and an almost complete assignment is achieved.

Vibrational spectra and assignment of acenaphthene- d10

Infrared and Raman spectra of single crystal samples of acenaphthene- d 10 have been recorded over the entire energy range of the fundamental vibrations. The spectra in all independent polarizations are presented. The analysis of the Raman spectra was assisted by the measurement of the depolarization ratios in carbon tetrachloride and benzene solutions. These data have been used to make firm assignments for most of the molecular fundamentals; however, this experimental assignment remains incomplete. The frequencies of the normal modes were calculated using a simplified valence force field transferred from other similar molecules. The experimental assignment is compared with this set of calculated values and the agreement is generally very good.

Infrared Studies on Rotational Isomerism. VI. Normal-Coordinate Analysis of 2-Chloro-, 2-Bromo-, and 2-Cyanoethanol

A normal-coordinate analysis of three substituted ethanol molecules X—CH2—CH2—OH (where X = Cl, Br, or CN) was carried out using the simple valence force field model, and a computer program of Schachtschneider translated into Fortran language by Brooks. The effect of internal hydrogen bonding was studied by adding one extra symmetry coordinate, H … X (two, H … C and H … N, in the case of 2-cyanoethanol). The corresponding force constants show a good correlation with the hydrogen bond strengths. Most of the other force constants maintain the same value in the gauche and the trans rotamers. In general the calculated fundamental frequencies agree closely with the observed ones. The potential energy distribution confirms the extensive coupling between certain vibrations; particularly the skeleton stretching and the CH2 twisting and rocking. Only the C—X stretching and the skeleton bending vibrations are strongly affected by rotational isomerism.

The vibrations of dibenzothiophene

Abstract Infrared spectra polarized along three orthogonal directions in single crystals of dibenzothiophene- h 8 and - d 8 have been recorded from 50 to 3500 cm −1 . The polarized Raman spectra of the single crystals have been measured in all possible orientations and this information has been supplemented by the measurement of depolarization ratios of the Raman lines in solution spectra. The frequencies of the normal modes were calculated using a simplified valence force field transferred from other similar molecules. The experimental assignment is compared with this set of calculated values and also with earlier assignments given carbazole and fluorene, and possible areas of doubt are located.

Valence Force Field Calculations for Octahedral Anions

Vibrational force constants for the octahedral anion AsF6−, SbF6−, SnF62−, and SnCl62− in the corresponding potassium salts are calculated using a simple valence force field treatment, with the intention of obtaining better agreement with recently reassigned bending modes in these compounds and to arrive at improved values for the inactive mode ν6[F2u].

Transferability of a simplified valence force field to pyrene and deutero-pyrene

Abstract The transferability of an approximate valence force field to pyrene is discussed and a criterion for grouping ortho, meta and para C—C—C—C interaction terms is proposed. From this force field, the i.r. and Raman frequencies of the planar vibrations of pyrene and deutero-pyrene are calculated and compared with experimental data. Several discrepancies are found between the calculated spectrum and the vibrational assignment previously reported in the literature.

The vibrational spectra of tetrakistrichlorophosphinenickel, Ni(PCls)4

The infra-red and Raman spectra of solid tetrakistrichlorophosphinenickel, Ni(PCl3)4, are reported, and the behaviour of the molecule in solution in organic solvents is investigated. Despite the instability of solutions of Ni(PC13)4, Raman polarization data could be obtained, confirming the assignment of the solid-state spectrum, and indicating that the molecular symmetry is consistent with the requirements of the Td point-group. A forceconstant calculation on the A1 block of frequencies was carried out using a simple valency force field, but owing to the neglect of possibly important interaction force constants little significance can be attached to the numerical results in terms of a discussion on bonding.

A vibrational assignment of acenaphthene

The Raman spectra of a single crystal of acenaphthene have been recorded in all possible orientations and this information has been supplemented by the measurement of depolarization ratios of the Raman lines in solution spectra. The polarized infrared spectra of an ac crystal section have been measured in the region below 600 cm −1 in order to complete the vibrational analysis in the low-frequency region. The frequencies of the normal modes were calculated using a simplified valence force field transferred from naphthalene and cyclo pentane. These calculated values were compared with an experimental assignment that was based on the assumption that deviations from an oriented-gas model were small.

On the vibrational assignment of thiophosphoryl fluoride

Normal coordinate calculations have been carried out for thiophosphoryl fluoride (SPF 3 ) using a simple valence force field and several modified valence force fields. These calculations have shown that the a 1 vibrations of SPF 3 cannot be assigned in a simple way to bending or stretching vibrations. The degenerate e vibrations on the other hand can be assigned to PF stretching FPF bending and SPF bending vibrations.

Complex halides of transition metals. Part VII. The vibrational spectra of the complex anions TiX62–, ZrX62–, and HfX62–, where X = Cl or Br

The solid-state far-infrared and laser Raman spectra of the salts [Et2NH2]2MX6, where M = Ti, Zr, or Hf, and X = Cl or Br, have been recorded. Force-constant calculations were carried out by employing a modified simple valence force field (MSVFF). For several of these salts the infrared-active modes ν3 and ν4 were found to be split.

Bending Frequencies and New Dimer Modes in the Far-Infrared Spectra of Transition-Metal Dihalides

This article describes measurements and analysis of the infrared absorption spectra of monomer and dimer species of the transition-metal dihalides in the region of 520–40 cm−1. Experiments have been carried out on MnCl2, FeCl2, CoCl2, NiCl2, and NiBr2 isolated in argon matrices at 4°K. For the monomers, the following ν2 bending frequencies (cm−1) have been observed: 83 (MnCl2), 88 (FeCl2), 94.5 (CoCl2), 85 (NiCl2), and 69 (NiBr2). In addition to these, the ν3 frequencies have been observed. These data are compatible with a linear structure, but in connection with other information, suggest that a simple valence force field is an inadequate description of the normal vibrations. For the dimers, the following frequencies (cm−1) have been observed and assigned on the basis of a bridge-bond structure of D2h symmetry: ν12 = 436.2 (Fe2Cl4), 432.5 (Co2Cl4), 440 (Ni2Cl4); ν11 = 289 (Co2Cl4); ν10 = 110 (Fe2Cl4); ν9 = 323 (Co2Cl4).

Fundamental frequencies and molecular configuration of biphenyl—II Normal coordinates

Both a modified Urey—Bradley Force Field and a Simplified Valence Force Field have been refined through a least square technique on the fundamental frequencies of biphenyl- d 0 and biphenyl- d 10 determined in a previous paper. A critical analysis of the obtained results is discussed. The description of the normal modes is obtained from Potential Energy Distribution and from atomic displacements. The problem of vibrations localized in ortho, meta and para position is discussed together with the problem of ortho hydrogen interaction. The results seem to indicate that the extent of delocalization of π-bonds across the inter-ring CC bond (conjugation), if it exists, it must be very small.

Far infrared spectra of charge-transfer complexes between iodine and substituted pyridines

Far infrared spectra of charge-transfer complexes between iodine and substituted pyridines, dissolved in cyclohexane, have been measured in the region 20 to 200 cm -1 . Bands have been assigned to the modified iodine molecule stretching vibration near 180 cm -1 , and to the stretching of the intermolecular bond in the range 65 to 95 cm -1 . The shifts of the vibration frequencies, and force constants calculated using a simple valency force field, have been discussed in relation to the mass, electronic and steric effects of substituent groups. Equilibrium constants for the formation of the complex have been determined. From the intensities of the absorption bands, further evidence has been found for a vibronic interaction, leading to a delocalization of the transition moment in the vibrations of the complexes, and to an enhancement of the intensity of absorption.

A simplified valence force field of aromatic hydrocarbons—I Normal co-ordinate calculations for C 6D 6, C 6D 6, C 10H 8, C 10D 8, C 14H 10 and C 14D 10

A simplified valence force field of aromatic hydrocarbons—I Normal co-ordinate calculations for C 6D 6, C 6D 6, C 10H 8, C 10D 8, C 14H 10 and C 14D 10

Vibrational spectrum of methylmercury(II) cyanide

Raman spectra of CH 3HgCN in the melt and in solutions of a range of solvents including H 2O, (CH 3) 2S and C 6H 6 have been obtained. Minor changes in the frequencies with medium were observed. The infrared spectrum of the solid has been recorded between 4000 and 300 cm −1. A complete assignment to vibrational modes corresponding to C 3c and a normal coordinate analysis based on a simple valence force field have been made.