Polarized Raman spectra and intensities of aliphatic amino acids

Raman spectra of aliphatic α-l-amino acids, glycine, alanine, and valine were re-investigated both in aqueous solution and deuterium oxide solution. The spectra were taken of the zwitterionic and of the completely deprotonated form of the amino acids. Spectra of leucine and isoleucine were studied in water at the isoelectric point. Spectra were recorded both with parallel and perpendicular polarization and the isotropic and anisotropic scattering components were isolated.The integrated intensities of CH stretch, CC stretch and carboxylate bend vibrations are discussed. Linear relations between the number of CC and CH bonds and the total scattered intensity in the appropriate spectral regions are observed. The sum over the carboxylate modes shows characteristic intensities for the first three members of the aliphatic amino acids.An increase of isotropic scattering of ϱ_co2 near 510 cm⁻¹ with increasing chain length of the amino acid (or with increasing concentration) is interpreted as the result of micelle formation.     

Rydberg bands in the UV spectrum of thiophene and its derivatives

The ultraviolet spectra of twelve halogenothiphenes have been recorded in the vapour phase. New transitions were observed in the region 45 000 to 50 000 cm⁻¹ which are absent in solution spectra and are assigned to Rydberg transitions. There is a good agreement of the band positions with those calculated from adiabatic ionization potential, using the quantum defect of thiphene. A study of the vibronic structure does not rule out the possible existence of two Rydberg-transitions. The vibrational frequencies of the fine structure are close to the observed values in the UP spectrum. The other members of the Rydberg series can be found in the far ultraviolet spectrum of thiophene.     

Polarized Raman spectra and intensities of aromatic amino acids phenylalanine,tyrosine and tryptophan

The prominent marker bands in the Raman spectra of the aromatic proteinogenic amino acids phenylalanine, tryptophan and tyrosine have been reinvestigated. Previous studies have been extended by measuring intensities against NaClO₄ as an external standard. Raman spectra were divided into isotropic (trace scattering of symmetric vibrations) and anisotropic (quadrupole scattering of antisymmetric or symmetric vibrations). These intensity and polarization properties of the marker bands were followed through pH changes from about 11–13 to 1–2.     

The intensities of the carbonyl bands in the infra-red spectra of 2- and 4-quinolones

The intensities of the carbonyl bands in the infrared spectra of sixty-five 2- or 4-quinolones have been measured. The results indicate that the high intensities of 2-quinolones distinguish them from 4-quinolones. Some applications in alkaloid chemistry are discussed, including proof that the ring system of maculosidine (XXVII) is linear.     

Absolute intensities of Raman trace scattering from bicyclo-[1.1.1]-pentane

Our previous theoretical studies have identified the Raman intensity parameter for the bridgehead C-H stretch in bicyclo-[1.1.1]-pentane as the largest for any saturated hydrocarbon yet considered, while the methylene C-H parameter is predicted to be ordinary. Theoretical methods including self-consistent field, static and time dependent density functional theory, and coupled cluster, all predict a large bridgehead intensity parameter, but differ widely in the actual value. We have synthesized bicyclo-[1.1.1]-pentane and recorded the absolute intensity Raman trace scattering spectra. The recorded intensity of a resonance polyad in the C-H stretching region has been resolved and distributed onto the fundamental modes through an anharmonic resonance analysis from a computed quartic force field. The experimental internal coordinate intensity parameters have been obtained and compared with those computed. Although the static and dynamic density functional values overestimate the parameter by 10%-18%, the values predicted at the coupled-cluster level are found to be correct to within experimental error.     

Raman,infrared and NMR spectra and structure of divinylmethylborane

The Rarnan spectra of gaseous, liquid and solid divinylmethylborane have been recorded from 20–3500 cm^?1 and the IR spectra of gaseous and solid divinylmethylborane recorded over the range 30–3500 cm^?1. A variable temperature study of the Raman spectrum of the liquid phase has been carried out. A complete vibrational assignment is presented. In the solid phase the molecule appears to have a planar heavy atom skeleton (C_s symmetry). From analysis of the spectra of the fluid phases, the presence of a second isomer, in which one or both of the vinyl groups are twisted slightly out of the BC₃ plane (C₁ symmetry), is proposed. Variable temperature ¹³C NMR studies have been carried out. A comparison of the ¹³C chemical shift of C_β of the vinyl group with the corresponding value in other vinylboranes indicates that relatively little delocalization of the π-electron density occurs in this molecule. Low temperature (?115°C) ¹³C NMR data are consistent with a low barrier to rotation about the boron-vinyl carbon bond.     

Observed bands in Raman and infrared spectra of 1,3-dioxolane and their assignments

We present a Raman study of liquid and polycrystalline dioxolane, together with data for a solid dioxolane/argon film. Observed bands are assigned to the bent conformer on the basis of ab initio calculated vibrations, accompanied with potential energy distribution. Two internal modes were calculated at 658 and 720 cm⁻¹ for the bent form. These were observed at 665 and 722 cm⁻¹ in liquid, and split into four bands (at 694, 697, 725, and 728 cm⁻¹) in the crystal at 10 K. In the solid dioxolane/argon film an additional band appears at 705 cm⁻¹ (between the bands at 675 and 726 cm⁻¹). A search for an additional dioxolane conformer trapped in argon was undertaken by performing molecular dynamics simulations of dioxolane/argon solid film and averaging overall molecular conformations. The resulting conformation did not correspond to an energy minimum, but indicated that changes of only a few degrees in dihedral angles could shift ring deformation and OCO bending modes for more than 10 cm⁻¹. Differential scanning calorimetric measurements gave evidence of solidification upon cooling at 146 K, and two phase changes on heating (one at 158.3 K, and a melting transition at 180.3 K). Further study is required on the hysteresis effect in the temperature behavior of dioxolane, and on the nature of the intermediate solid phase.     

Valence electron bands in the gas-phase x-ray photoelectron spectra of acetonitrile and nitromethane

The valence electron bands of the gas-phase X-ray photoelectron spectra were measured on acetonitrile and nitromethane. It is shown that the observed spectra can be interpreted successfully by comparison with the He I photoelectron spectra and the results of CNDO/2 calculations.     

An ab initio SCF calculation of the dipole-moment derivatives and infrared-absorption intensities of the water-dimer molecule

The dipole-moment derivatives and infrared-absorption intensities of the water dimer including several deuterated species have been calculated using ab initio SCF techniques. The results are compared with the analogous, quantities for monomeric water. In addition to the highly enhanced intensity of the intramolecular OH stretch most intermolecular modes that occur in the 90–600 cm^?1 region are also found to be very intense. An electrostatic model for the water dimer has been explored with a view to developing a possible scheme for the calculation of infrared intensities of larger clusters. As a result of the significant exchange and charge-transfer effects such a model is found to be unreliable in describing the dipole-moment derivatives that directly involve the hydrogen bond.     

Raman spectra and molecular structure of silicates

The frequencies of the strong Raman bands of silicates corresponding to the Si₂O ₅ ^2? complex anion and the SiO₂ molecule have been determined. This revealed the presence of these anions in silicates with double rings or double chains and various types of layers and the presence of SiO₂ molecules in silica modifications, feldspars, zeolites, and zircon group orthosilicates. A similarity between the Raman spectra of olivine group orthosilicates and garnet and phenacite group orthosilicates was found. This similarity was attributed to the existence of distorted tetrahedra in all of these groups, having disordered orientation in the garnet and phenacite groups.     

Resonance Raman spectra of β-carotene and its molecular structure in the excited electronic state

The resonance Raman spectra of β-carotene have been obtained at low temperature. The excitation profiles of ν₁ (1525 cm^?1) and 2ν₁ (3043 cm^?1) are analysed in terms of the Albrecht theory. The overlap integrals between the vibrational wavefunctions of the ground and the first excited electronic states are shown to be the most important factor in determining the resonance Raman intensities of this molecule. Information on the structure of the electronically excited state has been obtained.     

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.     

Vibrational spectra of stannane: Harmonic force field, Raman and IR intensities from ab initio correlated wavefunctions

The vibrational spectra and the harmonic force field for the stannane molecule has been calculated from ab initio SCF calculations using an effective core potential and two double-zeta basis sets for the valence electrons. Polarized functions and electron correlation effects on the calculated force constants and frequencies are analyzed carefully. At HF SCF level the calculated frequencies are higher than the experimental ones by about 8.15% while at second-order Møller-Plesset perturbation level, the mean absolute percentage deviation of the frequencies is found to be 3.75%. This mean absolute percentage deviation is notably improved at SDCI (3.2%) and SDQCI (2.2%) levels of theory. The integrated molar absorption coefficients and the scattering activities are calculated and their values agree reasonably with experiment.     

Raman spectra and structural characteristics of rare-earth element disulfides

Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 60–65, July–August, 1992.     

DFT study on the geometric, electronic structure and Raman spectra of 5,15-diphenylporphine

The ground state geometric, electronic structure and Raman spectra of 5,15-diphenylporphine (H(2)DPP) have been studied using B3LYP/6-31G(d) method and compared with that of well-studied free base porphine (H(2)P) and meso-tetraphenylporphine (H(2)TPP). Calculation shows that 5,15-substitution causes remarkable in-plane distortion, whereas the resulting out-of-plane distortion is negligible. The calculated electronic structure of H(2)DPP is consistent with the absorption spectra compared with H(2)P and H(2)TPP. The calculated vibrational frequencies of H(2)DPP scaled with a single factor of 0.971 agree well with experimental data (the rms error is 8.0 cm(-1)). The assignment of experimental Raman bands of H(2)DPP was discussed on the basis of theoretical calculation and the comparison with that of H(2)P and H(2)TPP. The splitting of some vibrational modes involving the motion of C(m) atom, such as nu(1), nu(8), and nu(10), was observed and was attributed to the diversification of the environment around C(m) atoms. As the shift of absorption peaks, the shift of some structure-sensitive Raman bands of H(2)DPP form that of H(2)TPP and H(2)P was attributed to the in-plane nuclear reorganization (IPNR) induced by phenyl-substitution, though the contribution of nonplanarity mechanism could not be excluded completely.