Vibrational spectra of tetramethyleyclobutane-1-one-3-thione and the fully deuterated derivative

Raman and i.r. spectra of tetramethylcyclobutane-1-one-3-thione (TMCBOT) and the fully deuterated derivative TMCBOT-_d¹² have been recorded. A fairly complete set of vibrational frequencies and assignments are given for the two molecules. The CO stretching mode was observed as a very strong Fermi doublet in the infrared spectrum of TMCBOT at 1811/1782 cm⁻¹. For TMCBOT-d₁₂ a similar doublet was observed at 1808/1775 cm⁻¹. The CS stretching mode was assigned to bands at 1303 cm⁻¹ for TMCBOT and 1307 cm⁻¹ for the deuterated molecule.     

Raman study of the molecular motions of pivalic acid: the liquid—plastic phase transition

Raman spectra of pivalic acid in the plastic and liquid phase have been measured. The reorientational correlation times have been evaluated from the ν_asCH, νCO and νCC bands as a function of temperature. The reorientational correlation time corresponding to ν_as CH and νCC bands is τ < 10⁻¹¹ s whilst for the νCO band τ = 4ps (T = 20°C). The calculated activation energy is 26 KJ mol⁻¹. The reorientation of the carboxylic groups which may be assisted by the proton transfer along the hydrogen bonds in dimers is discussed.     

1064-nm-excited Fourier transform Raman studies of bacteriochlorophyll-a in solid films and in a blue-green mutant of Rhodobacter sphaeroides

1064-nm-excited Fourier transform Raman spectra of bacteriochlorophyll-a (BChl) in various solid films and in chromatophores from a blue-green mutant of Rhodobacter sphaeroides have been obtained. The observed Raman spectra are free from high fluorescence backgrounds and sample degradation. The observed intensities seem to be enhanced because of a pre-resonant effect between the exciting radiation at 1064 nm and the Q_y absorption at 770–870 nm of BChl. The spectral features are substantially different from the Soret and Q_x resonance Raman spectra extensively investigated so far; several bands in the wavenumber region lower than 1200 cm⁻¹ are particularly enhanced in the Q_y pre-resonance Raman spectra. Bands due to both the C₂O and C₉O stretches appear at 1700–1620 cm⁻¹, providing structural information on these carbonyl groups. In the CC stretching region (1620–1490 cm⁻¹), the correlation between band positions and the co-ordination number of central magnesium, which was previously found in the Soret-excited Raman spectra, is preserved in the Q_y, pre-resonance Raman spectra as well. The relative intensities of strong bands in the 1200–1000 cm⁻¹ region appear to be useful for characterizing the BChl state. By using these advantages of the Q_y, pre-resonance Raman spectra, molecular interactions and arrangements of BChl in hydrated films and in the B870 light-harvesting complex of R. sphaeroides are discussed.     

Vibrational spectra of potassium hydrogen 2,3-furandicarboxylate and intramolecular H-bond

Infrared and Raman spectra of KHFur 2,3 and KDFur 2,3 are presented. An assignment of the bands is given which is in good agreement with previous results concerning acid salts possessing intramolecular hydrogen bonds. The ν_as OHO participation was observed at 670 and 520 cm⁻¹, absorption bands of medium intensity. The absence of a more pronounced broadening might be explained by assuming an anharmonic coupling between the ν_as OHO and the ν_s OHO modes, resulting in a combination band at 1000 cm⁻¹.     

Spectroscopic study of hydrogen bonding in the enol form of β-diketones—I. Vibrational assignment and strength of the bond

The i.r. and Raman spectra of the trans-enol form of some β-diketones and their deuterated analogues in α position are examined in the 4000-50cm⁻¹ range and an approximate assignment is given for the fundamental vibrations. The ν_as(OH) and ν(CO) values suggest that the intramolecular H-bond strength increases in the order: hexafluoroacetylacetone < trifluoroacetylacetone < acetylacetone < α - Cl - acetylacetone < benzoylacetone < dibenzoylmethane < tetraacetylethane.The observed relative Raman intensities of the ν(CC) and ν(CC) bands also support this feature. The spectroscopic results show a great change in the internal modes of the β-diketones upon deuteration; this behaviour indicates a greater localization of the π-electron system of the chelate ring and a weakening of the H-bond on deuteration. The ν_s(OH) vibration seems to be involved in one of the in-plane ring deformational modes.     

Zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzoxazole

The following zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzoxazole (L) have been prepared and studied by conductometric and i.r. methods: MLX₂ (MCd, XCl, Br; MHg, XCl), HgL_1.5X₂ (XBr, ClO₄), ML₂X₂ (MZn, XCl, Br, I, NO₃; MCd, Hg, XI, NO₃), ZnL₃(ClO₄)₂·2H₂O, CdL₃(ClO₄)₂·3H₂O. The frequency decrease of the ligand bands at 1614 and 1573 cm⁻¹ having a ν(CN) and the increase of the ligand band at 918 cm⁻¹ having a ν(CO) contribution indicate that in the complexes the ligand is N-bonded to the metal.     

Near infrared absorption spectrum of perfluoro-t-butanol/acetonitrile complexes at low temperatures: Fermi resonances and simultaneous transitions

Interactions between perfluoro-t-butanol (PFTB) and acetonitrile-d₃ (AN) in a mixture of freons are studied between 298 and 88 K in liquid or vitreous states. In the conditions of the experiment, a mean 1:2 stoichiometry [PFTB⋯(AN)₂] is inferred from previous matrix measurements. A ν_OH shift of about 160 cm⁻¹ is observed in this temperature range: it is mainly ascribed to solvent effects on the complex. In fact, the dν_OH/dT coefficient increases at low temperature on account of specific solvation of the complex by the freon Br atoms. The ν_OH + τ_OH combination wavenumber is little dependent on the state of PFTB, near 3900 cm⁻¹. A comparatively strong simultaneous transition involving the PFTB ν_OH mode and a ν_CN mode of neighbouring AN molecules is observed. Weaker bands could also be explained by such transitions involving a combination level of PFTB and a ν_CN vibration. Strong Fermi resonances are displayed in the 2ν_OH region when the ν_OH band is located around 3100 cm⁻¹, either in pure AN or in freons at low temperature. The levels interacting with 2ν_OH are ternary combinations and quaternary overtones mainly involving the COH bend and the CO stretch. These resonances are favoured by a strong increase of the OH stretching vibration anharmonicity.     

Vibrational anharmonicity and Fermi resonances in CHF2Cl

The infrared spectrum of CHF₂Cl has been recorded between 15 000 and 350 cm⁻¹. The Fermi resonance between levels involving ν₄ and 2ν₆ is analysed in bands extending from 800 cm⁻¹ to 7000 cm⁻¹ leading to a best value of k₄₆₆ = ± 14.98 cm⁻¹. In conjunction with the recent results of Amrein, Dubal and Quack, Molec. Phys. 56,727 (1985); estimates are reported for 38 out of 45 possible x_ij constants. A variation in the relative intensity of the two Q branches associated with ν₁, on cooling the gas cell, indicates that a hot band contributes to the upper branch at 3024.55 cm⁻¹. However, other evidence suggests that the latter arises also from the combination ν₂ + ν₇ + ν₉, in a very weak, close resonance with ν₁ at 3021.27 cm⁻. A number of anomalous band contours are reported.     

Spectra and structure of organophosphorus compounds—XXX. Vibrational and conformational study of methoxy difluorophosphinoxide-d0 and -d3

The i.r. (4000-40 cm⁻¹) and Raman (4000-10 cm⁻¹) spectra of gaseous, liquid and solid methoxy difluorophosphinoxide, CH₃OP(O)F₂, and the deuterated analog have been recorded. Results obtained from variable solvent and matrix isolation studies are consistent with the existence of both trans (CO bond trans to the PO bond) and gauche (dihedral angle approximately 120° from the trans form) conformers in the fluid phases. From simulations of observed gas phase i.r. band profiles, it was possible for assignments to be made to the individual conformers for a number of the fundamentals. Variable temperature studies carried out for the gaseous and liquid phases give energy differences between the gauche and trans conformers of 451 ± 100 cm⁻¹ (1.29 ± 0.3 kcal/mol) and 69 ± 20 cm⁻¹ (197 ± 57 cal/mol), respectively. Furthermore, these data are consistent with the gauche form being the thermodynamically preferred conformer for the gas phase whereas the trans conformer is preferred in the liquid phase and the only conformer present in the annealed solid. The methoxy torsional mode of the gauche conformer has been assigned to a very strong band observed in the far i.r. spectrum of the gas phase at 42 cm⁻¹. The matrix isolation spectra of the normal compound in Ar, CO and N₂ matrices indicated no changes in the conformational equilibrium among these different matrices and this equilibrium remains unchanged upon annealing the matrices.     

Theoretical study on the structures,force field,and vibrational spectra of cyclooctatetraene and cyclooctatetraene-d8

The structures and force field of 1,3,5,7-cyclooctatetraene (COT) have been studied using ab initio theory at the SCF level with the 4-21G basis set. The quadratic force field of the D_2d structure obtained by systematic scaling of the ab initio force constants successfully reproduces the observed frequencies of COT and COT-d₈ with a mean deviation of less than 10 cm⁻¹ for non-CH stretching modes. On the basis of the calculated results, assignments of the fundamental vibrations are examined. The normal mode υ₅ is reassigned to a weak band at 758 cm⁻¹ in the Raman spectrum of COT and to a weak band at 591 cm⁻¹ in the Raman spectrum of COT-d₈. The calculations favor the assignment of υ₂₆ given by Lippincott et al. [J. Am. Chem. Soc. 73, 3370 (1951)] over the revised assignment of Perec [Spectrochim. Acta 47A, 799 (1991)]. The calculations also furnish reliable prediction for the inactive A₂ fundamentals of COT and COT-d₈. The fundamental frequencies and IR and Raman intensities of ¹³CC₇H₈, which constitutes about 9% of COT in natural abundance, are also calculated. Only ν₁₀ (calculated at 908 cm⁻¹) of the formal inactive A₂ modes has appreciable Raman intensity (0.23 Å⁴/amu). A spectral feature due to this fundametal is identified in the liquid Raman spectrum of Tabacik and Blaise [C. R. Acad. Sci. Ser. II 303, 539 (1986)] as a weak peak at 908 cm⁻¹.     

Interactions intramoleculaires—XXXI. Etude vibrationnelle des conformères de chloro-4 et de cyano-4 cyclohexénes alkylés en 3

Infrared and Raman spectra in the liquid state of 3-R, 4-X cyclohexenes (R = CH₃, (CH₃)₃C; X = CN,Cl) and their d₁-(4) and d₃-(3,6,6) isotopic modifications, Raman spectra of some low temperature crystallised compounds, vibrational spectra in the solid state of cis and trans 1-acetoxy 3-t-butyl 4-cyano cyclohexenes, were studied.The frequencies of cyclohexenic skeleton modes below 900 cm⁻¹ and the frequencies of deformation modes involving the CCN bond or stretching νCCl vibration of the different conformers were assigned. In the cis and trans 1-acetoxy 3-R 4-cyano cyclohexenes (respectively in the e′a and e′e conformations), the positions of the 627 cm⁻¹ δ_ax and the 538 cm⁻¹ δ_eq deformation vibrations agree with the assignments proposed for the other cyano derivatives.     

Spectroscopic investigations of phase transition in 5-chloro-2-pyridone

Spectroscopic investigation of 5-chloro-2-pyridone has been carried out in the temperature range 77–300 K. At room temperature the ³⁵Cl NQR spectrum shows a single line at 35.618 MHz, but at 250.7 K two lines appear at 35.850 MHz and 35.840 MHz respectively indicating the presence of a phase transition. IR, far-IR, laser Raman and dielectric measurements have been carried out to investigate the phase transition further. Low temperature IR studies show splitting of ν(CCl), β(NH) and ν(CO) bands at T_c. Dielectric measurements show a small, but finite, change in the value of the dielectric constant around T_c. Raman spectra at different temperatures support the existence of a new phase, as shown by the appearance of a new band at 81 cm⁻¹, the frequency of which changes slowly as T_c is approached and which disappears at T_c. The temperature dependence of the NQR frequencies has been analysed using Bayer Kushida and Brown equations toevaluate the torsional frequencies.     

Vibrational spectra and structure of triphenyltin halides

The solid state IR and Raman spectra of SnPh₃Br do not show any band at 338 cm⁻¹, and there is not C_3ν point group inversion between ν_as SnC₃ and ν_s SnC₃ for SnPh₃X (X  Cl, Br). The presence or absence of a band around 338 cm⁻¹ in the IR spectra of triphenyltin compounds cannot be used to distinguish between pyramidal and planar SnPh₃ groups.     

Infrared transmission,attenuated total reflectance,and Raman spectra of potassium hydrogen succinate

The nature of the broad and strong absorption culminating near 950 m⁻¹ and of the bands in the 1600–1700 cm⁻¹ region is discussed with respect to polarized transmission, ATR, and Raman data obtained with single crystals of potassium hydrogen (and deuterium) succinate. The former absorption seems to be due to the B_u type OHO stretching combined with multiphononic components arising from transitions between the ν OHO and σ OHO branches for k ≠ 0. These appear to activate also the CO modes not allowed in the harmonic approximation for the C_2h factor group. Assignments for other bands are also given.     

Vibrational spectroscopic characterization of the phosphate mineral hureaulite – (Mn,Fe)5(PO4)2(HPO4)2·4(H2O)

This research was done on hureaulite samples from the Cigana claim, a lithium bearing pegmatite with triphylite and spodumene. The mine is located in Conselheiro Pena, east of Minas Gerais. Chemical analysis was carried out by Electron Microprobe analysis and indicated a manganese rich phase with partial substitution of iron. The calculated chemical formula of the studied sample is: (Mn_3.23, Fe_1.04, Ca_0.19, Mg_0.13)(PO₄)_2.7(HPO₄)_2.6(OH)_4.78. The Raman spectrum of hureaulite is dominated by an intense sharp band at 959 cm⁻¹ assigned to PO stretching vibrations of HPO₄²⁻ units. The Raman band at 989 cm⁻¹ is assigned to the PO₄³⁻ stretching vibration. Raman bands at 1007, 1024, 1047, and 1083 cm⁻¹ are attributed to both the HOP and PO antisymmetric stretching vibrations of HPO₄²⁻ and PO₄³⁻ units. A set of Raman bands at 531, 543, 564 and 582 cm⁻¹ are assigned to the ν₄ bending modes of the HPO₄²⁻ and PO₄³⁻ units. Raman bands observed at 414, and 455 cm⁻¹ are attributed to the ν₂ HPO₄²⁻ and PO₄³⁻ units. The intense A series of Raman and infrared bands in the OH stretching region are assigned to water stretching vibrations. Based upon the position of these bands hydrogen bond distances are calculated. Hydrogen bond distances are short indicating very strong hydrogen bonding in the hureaulite structure. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral hureaulite to be understood.     

High resolution i.r. spectrum of the ν1 band of HCCCl

The ν₁ spectrum of HCCCl was studied at a resolution of 0.045 cm⁻¹. Six bands were assigned and analyzed, two for the Cl³⁷ and four for the Cl³⁵ isotope. Band constants obtained for the six bands are listed. The ν₁ + ν₅ ← ν₅ band is unusually intense on the P side.     

Vibrational spectra and force constants of symmetric tops—XXII. Rotational analysis of ν2 + ν3 and ν1 + ν2 + ν3 of CF379Br and CF381Br

The rovibrational spectra of CF₃⁷⁹Br and CF₃⁸¹Br in the region of ν₂+ν₃ near 1120 cm⁻¹ and ν₁+ν₂+ν₃ near 2200 cm⁻¹ have been investigated with a resolution of 0.04 and 0.03 cm⁻¹ respectively. The rotational J structures have been resolved and were analyzed by means of polynomial and band contour simulation procedures. Molecular parameters (ν₀, x_ij, α^A,B) have been obtained from the analysis of the cold bands and the hot bands involving ν₆, 2ν₆, ν₃ and ν₅ for both isotopomers.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

Schwingungsspektren und Kiraftkonstanten symmetirischeir K]reisel—XVIII. Das Schwingungs-Rotations-Spektrum des CF3Cl im Bereich von ν4

The i.r. spectrum of gaseous CF₃Cl has been recorded in the ν₄ region near 1200 cm⁻¹ with a resolution of 0.08 cm⁻¹. The rovibrational band system has been analyzed by means of band contour simulation. It is shown that the irregular structure of the R branch arises from the two components of ν₄ + ν₆ - ν₆. A general theoretical treatment for hot bands ν_i + ν_j - ν_j is given where ν_i and ν_j belong to E species of point group C_3ν.     

Assignment and anharmonicity analysis of overtone and combination bands observed in the resonance Raman spectra of carotenoids

The resonance Raman spectra of all-trans carotenoids have been observed in the region of 5000-500 cm⁻¹ for samples in glassy solution at 77 K and in the in vivo state at room temperature. Prominent bands in the wavenumber region higher than 2000 cm⁻¹ are assigned to either overtones or combinations of three modes due to skeletal stretches and the CH₃ in-plane rock. From the wavenumbers of the observed Raman bands, anharmonicity constants for these three modes (including cross-term constants) are obtained. It is found that, for each carotenoid studied, the cross-term anharmonicity constant between the CC and CC stretches is significantly larger than the other anharmonicity constants.