Synthesis and Raman spectra of 3-deoxy-α-l-rhamnosides as model sugars of the Ascaris egg shell

The synthesis of two 3-deoxy-α-l-rhamnosides (i.e., 3,6-dideoxy-l-arabino-hexopyranosides) as models of ascaroside natural products is reported. The present approach is based on a Ferrier rearrangement from l-rhamnal, epoxidation of the resulting glycal and reductive opening of the isolated β-epoxide. The 3-deoxy-α-rhamnoside linked to a long aglycone chain was used to ascertain by Raman vibrational spectroscopy the presence of this peculiar sugar in the inner shell of Ascaris eggs.     

Comparative study of Raman and i.r. band widths of acetonitrile

Raman and i.r. band widths of all the vibrational bands of acetonitrile, CH₃CN and CD₃CN, have been measured in the pure liquid and in solutions of isotopic compounds. Widths arising from the vibrational relaxation, reorientational relaxation and resonance energy transfer have been separated on the basis of the current theories on vibrational band widths. The vibrational relaxation widths estimated for i.r. a₁ bands agree well with the observed isotropic Raman widths. Acceptable values of the rotational diffusion constants have been obtained from the band width data.     

Vibrational coupling in collision-induced raman scattering

The observed splitting of the collision-induced Raman band v₃ in liquid SF₆ is interpreted as vibrational exciton line splitting The bandwidth of the collision-induced Raman bands v₃ and v₆, in liquid SF₆ and v₂ and v₃ in liquid CO₂ and CS₂ can be explained by contributions from reonentational motion and from transition dipole-transition dipole vibrational coupling.     

Raman study of molecular dynamics of inorganic fluoroxidizers in nonaqueous solutions—Part 1. Xenon difluoride in acetonitrile

The Raman spectra of the totally symmetric ν₁(Σ_g⁺) mode of XeF₂ molecules have been measured in CH₃CN solutions at various temperatures and concentrations. The vibrational and rotational correlation functions as well as the characteristics times have been calculated. It was concluded that the vibrational band width in these solutions is to be attributed to the vibrational dephasing, whereas the contribution from the rotational relaxation has been found to be of less importance.     

Infrared and Raman multi-phonon spectra and structure of PbWO4

Improved Raman spectra of PbWO₄ show previously reported spectra contain large polarization and/or orientation errors. New spectroscopic information, obtained from polarized IR reflection and Raman spectra, allowed us to assign the IR and the previously unreported Raman multi-phonon bands. It was also used to show that it determines uniquely the C_4h factor group of PbWO₄. The use of IR reflection vs. infrared transmission spectra in the vibrational determination of crystal structures is also discussed.     

Infrared,Raman spectra and vibrational assignment of (PF2)2O

The IR spectra of gaseous and solid (PF₂)₂O has been recorded from 80 to 1200 cm^?1. The Raman spectra of gaseous, liquid and solid (PF₂)₂O have also been obtained (30–1000 cm^?1). The spectra of the fluid phases indicate the presence of at least two conformers. The spectrum of the solid phase can readily be interpreted on the basis of a single conformer possessing a symmetry lower than C_2v. A vibrational assignment is proposed for all normal modes except the PF₂ torsions. The results are compared with similar data of related compounds. There appear to be two molecules per primitive cell based upon the low-frequency Raman data.     

Structure and vibrational modes of AgI-doped AsSe glasses: Raman scattering and ab initio calculations

We report an investigation of the structure and vibrational modes of (AgI)_x (AsSe)_100−x, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As₄Se_n, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As₄Se_n molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe_mI_3−m provided useful information augmenting the interpretation of the Raman spectra.     

Reorientational and vibrational relaxation in liquid trichloracetonitrile

The first- and second-order reorientational correlation functions were determined from i.r. and Raman bandshapes of ν_s(CN)in liquid trichloracetonitrile and discussed in terms of the J-diffusion model. A consistent fit for G_1r(t) and G_2r(t) was possible for short times only (0–1.5 ps). The vibrational correlation functions, determined from Raman studies of the ν_s(CN) and ν_s(CC) bandshapes, are discussed in terms of recent theories of vibrational dephasing.     

Raman study of molecular dynamics of inorganic fluoroxidizers in nonaqueous solvents—Part 2. Xenon difluoride in hydrogen fluoride and bromine pentafluoride

The Raman spectra of the totally symmetric ν₁(Σ⁺_g) mode of xenon dilluoride molecules have been measured in HF and BrF₅ solutions at various concentrations. It is shown that the XeF₂ spectrum in HF has a complicated structure with three visible peaks. The complicated contour was resolved on elementary components which were identified. The vibrational and rotational correlation functions as well as the characteristics times have been calculated. It was concluded that the ν₁ vibrational band width of XeF₂ molecules in HF and BrF₅ solutions is to be attributed to the vibrational dephasing, whereas the contribution from the rotational relaxation has been found to be of less importance.     

Complete vapor phase assignment for the fundamental vibrations of furan,pyrrole and thiophene

Vibrational spectroscopic studies, including IR vapor, Raman vapor and Raman liquid spectra, have been made to obtain the complete set of fundamental vibrational frequencies in the vapor and liquid states for furan, pyrrole and thiophene. For furan, vapor values have been determined for the two previously ambiguous fundamentals, ν₁₁ and ν₁₈. Also determined is the vapor frequncy of two fundamentals of furan for which only the liquid value had been known. The fundamental vibrational frequencies of pyrrole have been completely determined in the gas and liquid states. The thiophene results confirm the assignment of Rico et al. [Spectrochim. Acta 21, 689 (1965)], although for several of the fundamental modes the vapor frequency is now measured. The Raman vapor spectra are conclusive concerning the refinements in vibrational assignment for furan and pyrrole, where virtually every binary combination band involving the out-of-plane fundamentals that yield an A₁ transition is observed. The Raman vapor results establish two significant Fermi resonances affecting fundamental vibration levels in pyrrole. Also, ¹³C and ³⁴S isotopomers are identified in the Q-branches of the Raman vapor spectra at natural abundance. A comparison of the spectroscopic and calorimetric ideal-gas thermodynamic properties is made. The differences are negligible in the region where the calorimetric data are most reliable.     

Synthesis, spectroscopic and structural properties of CF3SO2OCCl3

Trichloromethyl trifluoromethanesulphonate, CF₃SO₂OCCl₃, was prepared by quantitative reaction between Ag(CF₃SO₂O) and BrCCl₃. The conformational and structural properties of the gaseous molecule were studied by vibrational spectroscopy (IR (gas, liquid), Raman (liquid) and quantum chemical calculations (DFT and ab initio methods)).Theoretical and experimental vibrational results evidenced the presence of a single conformer with C₁ symmetry. This result is in agreement with the adopted geometry of covalent sulphonates. The conformational preference was studied using the total energy scheme and natural bond orbital partition scheme. Additionally, the total potential-energy has been deconvoluted using six fold decomposition in terms of a Fourier-type expansion.     

Infrarot- und Ramanspektren von Methylsulfonylhydroxylaminen

The i.r. and Raman spectra of 12 methylsufonylhydroxylamines and their O-, N- and C- deuterated derivatives were studied.The vibrational assignments were made on the basis of the isotope effects and an approximate normal coordinate analysis of CH₃SO₂N(H)OH and its deutero-compounds. The SN stretching mode is assigned to a strong band in the region 610–690 cm⁻¹.     

Infrared and Raman spectra of terephthalonitrile and terephthalonitrile-15N2. Force field for out-of-plane vibrations

A general assignment of the vibrational spectra of terephthalonitrile and terephthalonitrile-¹⁵N₂ is proposed on the basis of their infrared and Raman spectra. The relevant symmetry is found to be D_2h. The force field for the out-of-plane vibrations of these molecules was calculated by refining the general quadratic force field obtained by the semi-empirical MINDO/3 method, starting with a geometry optimized by this method. The refined force field reproduces the observed frequencies of the out-of-plane vibrations to better than ±0.5 cm⁻¹.     

Raman and infrared spectra of lanthanum molybdate

The infrared and Raman spectra of gel-grown lanthanum molybdate were recorded. Group theoretical analysis was carried out and a vibrational assignment proposed based on C_2h symmetry. Factor group and site effects are discussed.     

Electronic and resonance Raman spectra of iron(II)—tetraazamacrocyclic complexes containing N-heterocyclic ligands

The adducts of the meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,4,8,11-tetraene iron(II) complex with N-heterocyclic ligands exhibit three characteristic absorption bands in the ranges 690-640, 505-470 and 435-340 nm. Using excitation wavelengths coinciding with the low energy band, a selective enhancement of the Raman vibrational modes of the macrocyclic ligand is observed, supporting the assignment of a metal-to-diimine charge-transfer transition. The high energy band is strongly dependent on the nature and pK_a, of the axial ligands. Excitation at this band leads to the enhancement of the N-heterocyclic vibrational modes in the Raman spectra, indicating a metal-to-(N-heterocycle) charge-transfer transition. The intermediate band exhibits weak resonance Raman activity. Its intensity depends on the proximity of the high energy band and is consistent with the occurrence of an intensity stealing mechanism.     

Resonance Raman spectroscopy and DFT calculations of the protonation of 4-(2-pyridylazo)-N,N-dimethylaniline in solution and adsorbed on oxide surfaces

The protonation of 4-(2-pyridylazo)-N,N-dimethylaniline (PYAD) in aqueous solution and its adsorption on oxide surfaces has been studied by resonance Raman (RR) spectroscopy. The gas phase structures of neutral, protonated and diprotonated forms of PYAD were modelled by SCF-DFT calculations at the B3-LYP/DZ level, enabling determination of the simulated vibrational spectra of these species, together with vibrational assignments, and providing confirmation that protonation occurs initially at the pyridyl nitrogen atom. Electronic absorption spectra were interpreted using time-dependent DFT calculations. Adsorption of PYAD on SiO₂ or Al₂O₃ surfaces is mainly via the neutral species, hydrogen bonded to surface OH groups, although a small proportion of adsorbed molecules are protonated. By contrast, adsorption on SiO₂–Al₂O₃ results in complete protonation, indicating the presence of Brønsted acidic sites with pK_a values ? 4.5, whereas adsorption on H-mordenite results in diprotonation, indicating the presence of Brønsted acidic sites with pK_a values ? 2.     

Polarized Raman study of the Ce2(SO4)3·9(H,D)2O

The Raman spectra of oriented single crystals of cerium sulfate enneahydrate and that of its fully deuterated analogue are reported and compared. The role of the two types of lattice water molecules have been determined from the geometries of their immediate environments and consequent vibrational properties. The data obtained are subjected to certain geometric criteria to determine the orientations of the H₂O(C₁) and H₂O(C_s) molecules consistent with optimum interactions with their surroundings.     

Assignments of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene. Effect of the terminal and lateral methyl groups

The complete assignment of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene was obtained from a comparative analysis of their i.r. and Raman spectra (solid, liquid and gas) in the range 3200-50 cm⁻¹. It is shown that particular vibrational motions strongly interact to give rise to very characteristic modes depending on the site of methyl substitution. The comparison of our results with those of analogous shorter and larger polyenes and polyenals allows us to discuss the various local coupled motions characteristic of unsubstituted (CHCH CH)CH and methyl substituted (CHC(CH₃)CH), ((CH₃)₂CCH) or (CH₃CHCH) fragments in polyenic chains.