Vibrational spectra and torsional analyses of cis-2,3-dimethyloxirane and trans-2,3-dimethyloxirane

The Raman spectra of cis-2,3-dimethyloxirane and trans-2,3-dimethyloxirane in the vapor, liquid, and polycrystalline solid phases are reported for the region between 25 and 3100 cm^?1. The IR spectra of these two compounds between 80 and 4000 cm^?1 in the vapor and polycrystalline solid phases are also reported. In the IR and Raman spectra of gaseous trans-2,3-dimethyloxirane a total of eight torsional transitions have been observed. In the Raman spectrum of the cis compound in the vapor phase, four torsional transitions have been observed. From these experimental data, periodic barriers to the methyl torsional motions have been calculated to be 905 ± 7 cm^?1 (2.5 kcal mol^?1) for the trans molecule and 617 ±5 cm^?1 (1.76 kcal mol^?1) for the cis molecule. Additionally, complete vibrational assignments based on band contours, depolarization values, and group frequencies are proposed for both molecules and gas-phase thermodynamic functions have been calculated. These results are compared to the corresponding quantities for some similar molecules.     

Vibrational spectra and structure of the heptahydrodiborate ion, [B2H7]− in glycol ethers

The i.r. and Raman spectra of the heptahydroborate ion, [B₂H₇]⁻, and its deuterated derivative, [B₂D₇]⁻, have been obtained in solution and assignments have been made of the observed bands. The data are interpreted as indicating a bent C₂ structure in solution. Normal coordinate calculations based on this model are presented.     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.     

The molecular,electronic structures and IR and Raman spectra of metal-free,N,N′-dideuterio,and magnesium tetra-2,3-pyrazino-porphyrazines: Density functional calculations

A theoretical investigation of the fully optimized geometries and electronic structures of the metal-free (TPyPzH₂), N,N′-dideuterio (TPyPzD₂), and magnesium (TPyPzMg) tetra-2,3-pyrazino-porphyrazine has been conducted based on density functional theory. The optimized geometries at density functional theory level for these compounds are reported here for the first time. A comparison among the different molecules, including tetra-2,3-pyridino-porphyrazine (TPdPzH₂), phthalocyanine (H₂Pc) compounds, for the geometry, molecular orbital, and atomic charge is made. The substituent effect of the N atoms on these properties of these compounds is discussed.The IR and Raman frequencies and intensities for the three compounds have also been calculated at density functional B3LYP level using the 6-31G(d) basis set. Detailed assignments of the N–H, N–M, and pyrazine ring vibrational bands in the IR and Raman spectra have been made based on assistance of animated pictures. The isotope effect of D atoms are also discussed.     

Heteropoly compounds as octahedral high valence complex. Spectrochemical properties of Waugh-structure enneamolybdonickelate(IV) and enneamolybdomanganate(IV) ions

Electronic absorption and magnetic circular dichroism (MCD) spectra in UV-vis region of Waugh-structure [XMo₉O₃₂]^6?(X = Ni(IV), Mn(IV)) ion in aqueous solution and solid IR spectra have been measured. The Ni(IV) ion in the polyanion has a low-spin d⁶ electronic configuration and the Mn(IV) ion has a d³ configuration. Visible absorption spectrum of the nickelate(IV) polyanion is interpreted to be mainly governed by charge-transfer transitions of the “ligand”, Mo₉O₃₂, to Ni(IV) ion, rather than d-d transitions, while visible absorption of the manganate(IV) polyanion is governed, to a great extent, by d-d transitions. It is indicated by the MCD spectrum that the splitting of the first d-d absorption in the manganate(IV) polyanion is due to a contribution of the spin-forbiden transition, rather than from a trigonal splitting of the spin-allowed transition. Absorption and MCD spectra in UV region are due to charge-transfer transition within a common “ligand”, which are less influenced by the kind of heteroatom, Ni(IV) or Mn(IV). The MCD pattern by the intra-ligand charge-transfer is especially characteristic of the Waugh-structure polyanions.     

Vibrational spectra and normal coordinate analyses of the trimethyloxonium and trimethylammonium cations

Raman and i.r. spectra of the compounds (CH₃)₃O⁺ SbCl⁻₆ and (CH₃)₃NH⁺ SbCl⁻₆ are reported and assigned. Normal coordinate calculations support the vibrational assignments for the cations Of C_3v symmetry, and yield force constants k(CO) = 4.05 mdyn·Å⁻¹ and k(CN) = 4.80 mdyn·Å⁻¹ for the trimethyloxonium ion and the trimethylammonium ion, respectively.     

The conformation and vibrational spectra of isocyanato and isothiocyanatocyclohexane

The IR spectra of isocyanato and isothiocyanatocyclohexane (C₆H₁₁NCX) as liquids and as amorphous and crystalline solids at low temperatures have been recorded in the region 4000-50 cm^?1. High pressure (0–30 kbar) IR spectra of the neat samples were obtained in a diamond anvil cell and various high-pressure solid phases were studied. Raman spectra of the compounds as liquids and as low-temperature solids were obtained.Isocyanatocyclohexane crystallized directly as anisotropic solids containing equatorial molecules at low temperature and axial molecules at high pressure. Isothiocyanatocyclohexane formed a possibly plastic phase between 225 and 260 K where both equatorial and axial conformers are present. A solid high-pressure phase (1–3 kbar) at ambient temperature appeared anisotropic and contained both the e and a conformers. Below 225 K (atmospheric pressure) and above 10 kbar (ambient temperature) anisotropic crystals were formed which both contained equatorial conformers only.Normal coordinate analyses were carried out for the equatorial and axial conformers of the two molecules with different orientations (C_s and C_l symmetries) of the side chain. Force constants were transferred from various halo and pseudohalocyclohexanes. Tentative assignments of the fundamentals belonging to both the e and a-conformers are presented.     

Vibrational spectra of sodium gadolinium tungstate NaGd(WO4)2 single crystals: Observation of spatial dispersion

Room temperature polarized Raman scattering and infrared reflectance spectra of a NaGd(WO₄)₂ single crystal have been measured. The IR spectra interpretation was aided by a Kramers-Krönig analysis, and fitted to the independent oscillator model. All 13 theoretically expected Raman-active bands have been identified and assigned, as well as 7 out of 8 expected IR active bands. Splitting of bands in both Raman and IR clearly indicates a lowering of the crystal symmetry due to occupation disorder in the 4a site, that randomly accommodates either an Na⁺ or a Gd³⁺ ion. The reflectance IR spectra reveal a spatial dispersion, namely a dependence of the transverse optical (TO) polariton frequencies, on the propagation direction in the crystal. The crystal vibrational modes are correlated to the internal modes of the tungstate group WO₄^2?, and to the internal modes of the molecular skeleton. A detailed correlation map of the symmetry analysis is presented.     

Conformational analysis,barriers to internal rotation and vibrational assignment for dimethylethylamine

The IR (50–3500 cm^?1) and Raman (20–3500 cm^?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol^?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH₃ rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol^?1, whereas the barrier for the CH₃ rotor of the ethyl group has been calculated to be 3.71 kcal mol^?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm^?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines.     

The low-frequency Raman and IR spectra of nitric acid hydrates

The low-frequency region of the infrared and Raman spectra of nitric acid hydrates is analyzed. Theoretical calculations of the vibrational normal modes of the crystals of nitric acid monohydrate and the β-phases of the dihydrate and trihydrate are carried out, focusing the results in the regions below 175 cm⁻¹ and near the symmetric stretch of the nitrate ion NO₃⁻, around 1000–1100 cm⁻¹. A prediction of the corresponding infrared spectra is presented. A joint study is performed of the calculated normal modes, the predicted IR spectra, and the recently published Raman spectra of these compounds, based on symmetry considerations and using the atomic displacements associated to each normal mode as a further source of information. Although most of the modes present a strong mixture of atomic motions, assignments can be proposed for some of the vibrations.     

Time-resolved resonance raman spectra and decay kinetics of triplet anthracene in fluid media

Reported here are the time-resolved resonance Raman spectra and decay kinetics of the lowest triplet state (³B_2u⁺) of anthracene-h₁₀ and anthracene-d₁₀ molecules in fluid media at room temperature. The triplet population (≈3 × 10^?5 M) is observed to decay at microsecond times by triplet—triplet annihilation. Vibrational assignments for the observed Raman bands are proposed.     

IR and Raman investigations of structures and phase changes in scandium fluorides

Crystallographic data and IR Raman spectra are presented for a new series of compounds, M₃ScF₆ (M Na, K, Rb, Cs, T1). Spectral assignments are proposed and effects of the cation on vibrational modes is discussed. Preliminary temperature-dependant Raman spectra are presented and correlated with DSC and crystallographic data.     

Raman Combinations and Stretching Overtones from Water, Heavy Water, and NaCl in Water at Shifts to ca. 7000 cm−1

Photographic Raman spectra were obtained at shifts to ca. 7000 cm^–1 for pure water and for a saturated aqueous solution of NaCl using argon ion laser excitation. Raman spectra were also obtained photoelectrically for H₂O and D₂O between ca. 2500 and ca. 7000 cm^–1 using 248-nm excimer laser excitation and boxcar detection. Overtone and combination assignments are presented for H₂O and D₂O. The first IR OH-stretching overtone from water occurs 215 cm^–1 above the first Raman OH-stretching overtone because the IR overtones are dominated by asymmetric stretching. The second OH-stretching Raman overtone from water is estimated to occur near 10,020 ± 20 cm^–1, with 9950 cm^–1 as a lower limit.     

Vibrational spectra of solid tri-μ-carbonyl-(hexacarbonyl)di-iron(O), Fe2(CO)9

Laser Raman spectra of solid tri-μ-carbonyl(hexacarbonyl)di-iron(0), Fe₂,(CO)₉, have been recorded at 295, 100 and 15 K using a surface scanning technique to avoid sample decomposition. The data indicate that no phase change occurs throughout the temperature range studied. The room temperature IR spectrum of the solid was also investigated in the 700-350 cm^?1 region. The vibrational assignments proposed are in good agreement with the factor group predictions for the known P6_3/m (C_6h²) space group symmetry of the crystal.     

Frequences infrarouges et Raman caracteristiques de cyclopropyl- et (cyclopropylmethyl)trimethylsilanes: Comparaison avec les vinyl- et allyltrimethylsilanes—III

The i.r. and Raman spectra of 20 compounds with a trimethylsilyl group linked to either a cyclopropane ring or a vinyl or allyl radical have been recorded between 400 and 4000 cm⁻¹. The experimental results and the vibration frequency assignments, especially the symmetrical SiC_n stretching, show that there are two classes of derivatives characterized by analogous SiC spectra: (1) the vinyl- and cyclopropyltrimethylsilanes and (2) the allyl- and (cyclopropylmethyl)trimethylsilanes. The spectroscopic behavior of each class is consistent with its observed chemical reactivity. A distinction can also be made between some structural isomers on the basis of the SiC stretching or other frequencies.     

The vibrational spectrum of (maleic anhydride)iron tetracarbonyl

On the basis of solid-phase IR and Raman spectra, with some solution data for the IR, a reasonably complete vibrational assignment has been made for the modes of maleic anhydride in (maleic anhydride)iron tetracarbonyl. Shifts in v(C=C) and δ(CH) are consistent with a strong interaction with the metal, but relatively little coupling between the modes. More restricted assignments were made for modes associated with the (maleic anhydride)iron and Fe(CO)₄ fragments.     

Vibrational spectra and normal coordinate calculations for dimethyltelluride-d0, -d6 and dimethyltellurium difluoride-d0, -d6

The i.r. (4000-30 cm⁻¹) and Raman (4000-O cm⁻¹) spectra of dimethyltelluride, dimethyltellurium difluoride and their deuterated analogs have been obtained. All the active fundamentals of these compounds except methyl torsions were assigned, assuming a C_2υ molecular symmetry for both the tellurides. Normal coordinate calculations have been made in order to confirm the proposed assignments. The skeletal bond strength of the tellurides together with that of TeF₄ are discussed, using the valence stretching force constants.     

Infrared matrix-isolation spectra of monomeric oxalic acid

Infrared spectra of monomeric oxalic acid-h₂, -hd and -d₂ have been observed using neon matrix-isolation spectroscopy. In addition, spectra of oxalic acid-h₂, vapor were obtained using a heated absorption cell with a 10 m pathlength. All IR active fundamentals are assigned for oxalic acid-h₂, and -d₂, except the low frequency torsion. The spectra are interpreted in terms of the C_2h intramolecularly hydrogen bonded model. Two vibrational assignments are discussed; one involves a very large intensity for the v₈ + v₁₁ (COH torsion) combination band of oxalic acid-h₂. Tentative values for several Raman active fundamentals of oxalic acid-h₂ are suggested using possible combination bands. Few fundamentals of oxalic acid-hd correlating with the Raman modes of the symmetric monomers could be observed. A force constant analysis of the by secular block is presented.     

Spectroscopic studies of mixed hexa-hepta scandium fluorides

IR and Raman spectra are presented for three new compounds which contain ScF₆⁻³ octahedra and ScF₇⁻⁴ pentagonal bipyramids, KSc₂F₇, RbSc₃F₁₀ and Rb₂Sc₃F₁₁. Spectral assignments are proposed and discussed in view of the assumption that these compounds are isostructural with the analogous indium series. The group-theoretical analysis for one of the compounds demonstrates the reduction in the number of vibrations due to atom sharing.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 78[1]Ergänzende Informationen von “polarisierten” Raman‐Spektren orientierter Einkristalle und Modellrechnungen auf der Grundlage der Dichtefunktionaltheorie bei der Zuordnung der Schwingungsspektren von Decamethylosmocen

The far and mid infrared (FIR/MIR) spectra of powdered Os(η⁵‐C₅Me₅)₂ (OsCp*₂) as well as the polarized Raman spectra of an oriented single crystal (where the two molecules of D_5h symmetry in the unit cell are uniformly oriented) have been recorded. The latter allow the assignment of the observed Raman lines to irreducible representations (irreps) which agree well with the predictions of a calculation applying density functional theory. This finding suggests additional correlation of the observed (unpolarized) bands in the FIR/MIR spectra with the calculated wavenumbers (and their irreps) of IR active normal modes. Neglecting νCH vibrations an r.m.s. deviation of 15.8 cm^–1 for 40 assignments (Raman and IR) could be achieved. Skeletal and intra‐ligand vibrations could be identified and a number of previous assignments of the latter had to be revised. Because of mixing with skeletal modes some of the low frequency intra‐ligand vibrations display a noticeable dependence on the mass of the central atom which prevents the direct transfer of the identified γCCH₃ and βCCH₃ normal modes from MCp*₂ (M = Fe, Ru, Os) to LnCp*₃ (Ln = La, Ce, Pr, Nd, Sm) complexes.