Systematics of the librational modes of water in the IR spectra of MSO4 · H2O (M = Mn,Co, Ni,Zn)

In the isomorphous hydrates MSO₄ · H₂O (M = Mn, Co, Ni, Zn), where M-O_W distance is the only variable, the frequencies of the wagging, rocking and bending modes of water and of metal-oxygen stretching have been shown to correlate smoothly with the distance r(M-O_W). Quantitative relations have been found for ν_W and ν(M-O_W) which vary linearly, while ν_R and ν^C₂ vary non-linearly with r(M-O_W).     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.     

Force constants,vibrational assignment and geometry of methyl amine from hartree—fock calculations

The force constants and geometry of CH₃NH₂ have been calculated from Hartree—Fock wave-functions by the force method, using a 73/3/1 Gaussian basis set. The fundamental frequencies obtained from the ab initio force constants corroborate the assignment of Gray and Lord except for the uncertain A″ NH₂ twisting and CH₃ rocking frequencies. The results indicate that the 1335 cm^?1 band in CH₃NH₂ is v₁₃, the antisymmetric combination of these modes, and that their symmetric combination, v₁₄, is located between 880 and 1000 cm^?1. The calculations reproduce the experimentally observed tilting of the CH₃ group toward the lone pair on nitrogen.     

Spectra and structure of gallium compounds: Part VI. Infrared and Raman spectra of trimethylgalliumtrimethylphosphine

The infrared (50–4000 cm^?1 ) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaP(CH₃)₃ have been recorded for the solid state at the temperature of boiling liquid nitrogen. The spectra have been interpreted on the basis of C_3v molecular symmetry and a complete vibrational assignment except for the methyl torsional modes is presented. A modified valence force field model has been utilized in calculating the frequencies and potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis acid and the Lewis base moieties and the differences are shown to be consistent with structural changes upon adduct formation. Extensive coupling has been observed between the Ga-P stretching mode and the PtC₃ and GaC₃ deformational modes. Substantial coupling is also observed between the PC₃ and the GaC₃ rocking motions. The magnitude of the Ga-P stretching force constant is found to be much smaller (0.88 mdyn Å^?1) than that reported for (CH₃)₃PGaH₃ and the difference possibly reflects the relative stabilities of the donor-acceptor bond in the two complex species.The fact that none of the A, modes appear as doublets in the spectra, nor are any of the E modes split except for the GaC₃ antisymmetric stretch, which is believed to be due to the two isotopes of gallium, indicates that there is only one molecule per primitive cell sitting on a C_3v or C₃ site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Vibrational relaxation of ethylene oxide and ethylene oxide-rare-gas mixtures

The collision-induced vibrational energy relaxation of ethylene oxide (C₂H₄O) was studied by means of laser-induced fluorescence. The time-dependent population of the vibrational modes v₃ and v₅/v₁₂ was measured after excitation of CH-stretching vibrations near 3000 cm^?1. Rate constants for the vibrational energy transfer by collisions with C₂H₄O and the rare gases are deduced, and a simplified model for the vibrational relaxation of C₂H₄O is discussed.     

A general quadratic force field for the diazirine molecule

A general quadratic force field has been calculated for the vibrations of the diazirine molecule by the refinement of a series of force constants obtained recently ab initio by Wiberg et al. for cyclopropene. The calculated force constants have been refined to fit the frequencies for the H₂CN₂ and D₂CN₂ species and the isotopic shifts of the H¹³CN₂ and H₂C¹⁵N₂ species.     

Energy dependence of the S1 -decay of propynal and propynal-d1 and the influence of collisions

The collision-free lifetime and the quenching rate of S₁(¹A″) vibrational levels of propynal and propynal-d₁ have been measured in the pressure range O.1-1OmTorr at room temperature. The collision-free decay of propynal is dominated by internal conversion that of propynal-d₁ by fluorescence. In both molecules the internal conversion rate is dependent on specific vibrational modes, in particular of the most efficient promoting mode v₁₀[CH(ald) wagging mode]. The intersystem crossing process of propynal, inefficient at the vibrationless S_1, level, remains unimportant at least up to an excess energy ≈ 3000 cm^-1. The quenching of the fluorescence is due to a very efficient collision-induced intersystem crossing (130 <σ_ISC^cl ? 600 A²). The strongly varying rates of this process, apparently dependent on the vibronic level, have been measured with propynal (propynal-d₁), argon, and butane as collision partners.     

MF2 vibrations and librations of water molecules in the series MF2·4H2O (M = Fe,Co, Ni or Zn)

The infrared absorption spectra of the series MF₂·4H₂O (M = Fe, Co, Ni or Zn) and of the respective deuterates were recorded at 296 and ∼ 100 K in the 1200-400 cm⁻¹ wavenumber region. Using the known ZnF₂·4H₂O structure as a model, the number of i.r. active librations and MF₂ vibrations was predicted with the aid of a group theoretical treatment. The librations were distinguished from the MF₂ and MO vibrations and assigned, using isotopic ratios and correlations between the unit cell volumes, the uncoupled OH and OD stretch vibrations of HDO and the twisting libration. The six librations are assigned to two types of water molecules with low symmetry and with different hydrogen bond strengths, and are compatible with an orthorhombic Pca2₁ structure. The v₁ and v₃ intramolecular MF₂ vibrations are assigned, using ZnF₂·4H₂O crystal data and matrix-isolated v₁ and v₃ (v_1.3) values as guide. Shifts of v_1.3 and v₁/v₃ relative to the matrix-isolated values suggest smaller MF bond lengths. The shifts in the values of v_1.3 and v₁/v₃ upon deuteration and lowering of the temperature indicate smaller MF bond lengths and FMF angles.     

IR matrix spectra of CsNO2, RbNO2, KNO2, and NaNO2. The structure of CsNO2

The IR spectra of alkali nitrites were studied in Ar matrices at the temperature of 7 K. The spectra of CsNO₂ were investigated with the aid of ¹⁵N and ¹⁸O isotopes in order to determine the structure of the gaseous molecules. The IR spectra of ¹⁸O-enriched CsNO₂ samples were recorded and the results interpreted by means of normal coordinate calculations. CsNO₂ has a planar ring structure of C_2v, symmetry. The bond angle ONO of this molecule was calculated to be 116 ± 5°. NaNO₂ as well as the remaining alkali nitrites have C_2v, symmetry structures. Far-IR spectra of alkali nitries were recorded in order to measure the interionic stretching vibrations; in some case low-frequency bands were observed and assigned to the A₁ and B₁ interionic stretching modes.     

Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

A normal coordinate analysis of monomethylhydrazine and its bidentate nickel (II) chloride complex

A full normal coordinate analysis (NCA) has been carried out on monomethylhydrazine and N-deuterated monomethylhydrazine. The C_3ν symmetry of the methyl group is lost; nevertheless the concept of specific methyl group modes is still valuable. The NN stretching mode is relatively pure enabling it to be used as a criteria of coordination. An NCA has also been carried out for the bidentate nickel complex NiCl₂(NH₂NHCH₃)₂. Interesting effects are observed for the wagging and twisting modes of the NH₂ group on coordination.     

The vibrational spectra of maleimide and N-D maleimide

The infrared spectra of maleimide as a vapour (160°C), melt (100°C), oriented polycrystalline film, pellet and when dissolved in various solvents were recorded between 4000 and 400 cm^?1. Also certain spectra in the far infrared region 400-40 cm^?1 were obtained. Raman spectra of the crystalline solid, melt and as a saturated solution in acetonitrile were recorded and semiquantitative polarization measurements carried out. For N-D maleimide infrared and Raman spectra of the solid compound were recorded.The fundamental frequencies have been assigned in terms of C_2v, symmetry on the basis of infrared vapour contours and dichroism of the oriented film as well as on Raman polarization data. A force field was derived for maleimide, by initially transferring force constants from maleic anhydride and subsequent refinement of the force constants. The agreement between observed and calculated frequencies for the in-plane modes was satisfactory whereas certain large discrepancies remained for the out-of-plane vibrations.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Vibrational Spectra of the Cyclic SN-Compounds S4N4, S4N4H4 and S3N3Cl3

The IR and Raman spectra of solid and dissolved S₄N₄, S₄N₄H₄, S₄N₄D₄ and S₃N₃Cl₃ have been recorded and are assigned according to D_2d, C_4v and C_3v symmetry respectively. In the solid state, many forbidden bands and splittings of degenerate vibrations are observed because of the symmetry lowering in the crystals. Due to the different size and shape of the rings and to strong coupling of the normal modes there is no clear correlation between the SN ring stretching vibrations and the strength of the SN bonds, except for the one of the E modes. However, the stretching force constant show the trend expected from changes in interatomic distances.     

The vibrational spectra of N-Cl maleimide

The infrared spectra of N-Cl maleimide as a Nujol mull and dissolved in various solvents were recorded between 4000 and 30 cm^?1. Raman spectra of the crystalline solid and saturated solution in CH₃CN were recorded and semiquantitative polarization measurements were made.The fundamental frequencies have been tentatively assigned in terms of C_2V symmetry, based upon Raman polarization data and analogies with the spectra of maleimide and maleic anhydride. A force field was derived by initially transferring force constants from maleimide. After small iterations a satisfactory correspondance was achieved between the observed and calculated in-plane modes whereas larger discrepancies remained for some of the out-of-plane vibrations.     

Infrared and Raman spectra and normal coordinate calculations for methylisothiocyanate

The infrared spectra (3200-50 cm^?1) of gaseous and solid CH₃NCS and CD₃NCS and the Raman spectra (3200-10 cm^?1) of the liquids and solids have been recorded. The spectra have been interpreted on the basis of a “pseudo-symmetric top” with C_3v symmetry. An assignment of the fundamental vibrations in both molecules, based on their infrared band contours, depolarization values and group frequencies, is given and discussed. Particularly interesting is the low-frequency region where band maxima were observed at 152 and 80 cm^?1 for CH₃NCS and 139 and 71 cm^?1 for CD₃NCS in the infrared spectra of the gases. A normal coordinate analysis has also been carried out based on C_3v symmetry. Considerable mixing was found between the C_αN stretch and NCS symmetric stretch in both isotopic species. The other normal modes in CH₃NCS are reasonably pure but, for the CD₃NCS molecule, considerable mixing was found between the CD₃ stretches and NCS antisymmetric stretch. The proposed vibrational assignment and the results of the normal coordinate calculations are discussed and compared with the results obtained for similar molecules.     

An infrared study on Langmuir–Blodgett films of 14,15-bis(hydroxyimino)-13-thiaoctacosane

The Langmuir–Blodgett (LB) films of 14,15-bis(hydroxyimino)-13-thiaoctacosane (TOC) on aluminium plated substrates were investigated using Fourier transform infrared (FTIR), grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. The LB films of TOC can be transferred onto the solid substrate successfully. The molecular structure of LB films was analysis by comparing the GAIR and HTAR spectra. The intense bands at 2848 and 2918 cm⁻¹ are assigned to symmetric ν_s(CH₂) and asymmetric ν_a(CH₂) stretching vibrations of methylene groups. These peaks suggest that the alkyl chains in TOC are nearly in all-trans conformational state. The presence in the infrared spectra of several bands due to the methylene wagging and twisting modes and of the splitting of the bands due to the methylene scissoring mode at 1467 and 1459 cm⁻¹ and the CH₂ rocking mode at 720 and 731 cm⁻¹ also indicates that in films of TOC alkyl chains are in the all-trans conformation and packed in either an orthorhombic or a monoclinic structure with an orthorhombic subcell containing two mutually orthogonal molecules. Another conclusion presented in this paper that the alkyl chain tilt, which is the angle between the axis, which bisects the C–C bonds and the surface normal, was quite large by comparing the GAIR and HATR spectra.     

Pseudo-exact force constants by the high and low frequency separation method

A method based on the “Approximate Separation of High and Low Frequencies” by Wilson et al. is developed and applied to molecules with three vibrations in a single species. It is shown that for a number of ZXY₃ (C_3v), ZXY₂ (C_2v), and ZXY (C_s) type molecules, for which exact force constants and isotopic data are available, this method—when used in conjunction with the isotopic data-reproduces the exact force constants of the reduced secular determinant. The high and low frequency separation seems to be a good method for determining the force constants in many n = 3 cases, where the highest and/or lowest frequency vibrations are rather characteristic and where—as in most cases—isotopic frequency data alone are insufficient for the determination of the exact force field. Extension to higher order secular determinants should also be possible.     

Vibrational spectroscopic studies on some 2-substituted 1,3-dithi a-2-boracyclopentanes

Infrared and Raman spectra are reported for 2-X-1,3-dithia-2-boracyclopentanes, where X = Br, Cl, Ph or NMe₂. In all cases the vibrations of the heterocyclic ring unit can be assigned in terms of C₂ symmetry, corresponding to a “twisted-ring” conformation similar to that found for the related molecule 1,3-dithiolan-2-thione. The internal modes of the B-Ph unit are in agreement with C_2v “local” symmetry, while those for B-NMe₂ suggest a considerably lower symmetry.     

Infrared and Raman spectra of lithium trihorate: Vibrational assignments and a correlation with its nonlinear optical activity

Infrared and polarized single crystal Raman spectra of lithium triborate (LBO; LiB₃O₅) are reported and analysed. All four (A₁, A₂, B₁ and B₂) symmetry species of the C_2v, point group isomorphic to the C_2v⁹(Pna2₁) space group are Raman active in distinct crystal polarization experiments. A complete set of symmetry assignments based on a factor group analysis is presented. The internal and external vibrations are separated on the basis of frequency and the observation that the magnitude of the correlation splitting for the internal modes is very small. A comparison of the internal frequencies of various borate species suggests a correlation between the B-O stretching frequency and the nonlinear optical efficiency of the material.