Isotopic mixed crystal exciton spectra in the far infrared: Naphthalene

The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene-h₈ and d₈ were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B_3u, A_u and B_1u vibrational exciton bands were found to be in the separated band limit. The lowest energy B_3u “butterfly” mode with its large (15 cm^?1) exciton splitting was found to agree well with CPA calculations of mixed crystal spectra. A peak at 185 cm^?1 was also assigned as a peak in the vibrational exciton density-of-states of the B_3u mode.     

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.     

Triplet-triplet absorption spectra of phenanthrene and azaanalogues

Triplet-triplet (T-T) absorption spectra of phenanthrene and several azaanalogues were measured in the spectral range from 25000 to 17000 cm⁻¹ at 83 K. For the first time a vibrational structure of the main band systems in the T-T spectra could be detected. The vibrational modes producing these progressions are associated with the lower T₁ state. The assignment of the vibrational structure to the T₁ state has been confirmed by computation of the T-T spectra with the help of a lineshape function. Furthermore, in the spectra of the azaanalogues an additional absorption band appears which is assigned to a T-T transition from the T₂ state.     

Tunable biode laser high resolution spectroscopy of the ν3 vibration of matrix isolated SO2

True lineshape of the ν₃(b₁) vibrational transition of ³²SO₂ isolated in an Ar matrix was measured with a high resolution (< 10^?3 cm^?1) tunable diode laser spectrometer and temperature effects on line frequencies and linewidths are reported.     

Decay of vibrational coherence in ortho-para mixtures of solid hydrogen

Hydrogen crystals were pumped by stimulated Raman gain into coherent superpositions of the ground and 2 v = 1 vibrational exciton state and its amplitude monitored by coherent anti-Stokes scattering. The resulting non-exponential and temperature independent (1.6–4.2 K) decays, for o-H₂ concentrations between 0.22 and 2.7%, were attributed to compositional scattering.     

Raman and NMR study of parallel reorientational diffusion in nitromethane

Raman spectral bandshapes of the ν₇, antisymmetric CD₃ stretching mode, and deuterium spin-lattice relaxation times in nitromethane-d₃ were measured as a function of temperature in the liquid-phase. Perpendicular diffusion coefficients (D_⊥) calculated from dielectric and ¹⁴N relaxation times in the literature were in excellent agreement at all temperatures. Unlike earlier studies in acetonitrile and iodomethane, parallel diffusion constants (D_z.snfc;) determined from the Raman lineshape were substantially greater than those calculated from T₁(²D), possibly resulting from broadening of the vibrational band due to hydrogen bond interactions. Also in contrast to the earlier investigations, values of D_z.snfc; obtained from both methods were substantially lower than coefficients calculated from the Free Rotor model of reorientation, providing clear evidence that intermolecular self-association slows the spinning motion of nitromethane in the liquid-phase.     

Theory of excimer vibrational relaxation and U.V. emission in solid neon

A quantitative explanation is provided for the observed UV emission from Ne₂^* molecules in solid neon. An expression involving only known molecular quantities and lattice parameters is given for the rate of vibrational relaxation of an excimer, initially formed in a highly excited level, by interaction with the phonons. This expression is used to show that relaxation cannot proceed to the ground vibrational level of Ne₂^* during the radiative lifetime of the excimer (at the low temperatures at which the experiments are done). The calculation brings out that the vibrational population is concentrated at the n = 3 level when radiation takes place. The lineshape for dissociative UV emission from the n = 3 state of the excimer is computed, and found in very good agreement with experiment.     

Accurate measurement of the pressure broadening of the ν1 Raman line of CH4 in the 1–50 atm region by inverse Raman spectroscopy

The lineshape of the ν₁ Raman band of methane is measured as a function of pressure between 1 and 50 atm by inverse Raman spectroscopy using the 488 nm output of a cw Ar⁺ laser as a probe beam and the output of a pulsed dye laser as a Stokes pump beam. The linewidth is found to increase linearly in this pressure region, and the fwhm Δν (in cm^?1) can be expressed as Δν = 0.32 + 0.012p, p being the methane pressure in atm.     

Coherent amplification in fluorescent dye solutions. II. The inverse pre-resonance Raman spectrum of rhodamine 6G

Inverse pre-resonance Raman spectra of rhodamine 6G in solution in methanol have been recorded over the concentration range 10^?1 to 10^?4 mol ?^?1. The solute and solvent transitions are found to display perfectly normal lorentzian profiles over the whole of this concentration range. Intensities and depolarization ratios of the pre-resonance Raman features are recorded. It is shown that the spectra arise from monomeric rhodamine 6G molecules in the singlet electronic ground state and the relative merits of the CARS and inverse Raman methods for recording resonance Raman spectra are discussed.     

Inter-sublattice energy transfer in MnF2

The magnetically induced circular emission (MCE) of an exciton—magnon pair from the third nearest neighbour impurity trap [Mgσ(III)] in MnF₂ shows an unusual lineshape. The field dependence of the MCE suggests that this is a consequence of a magnon assisted transfer of excitation between sublattices via the intrinsic exciton band.     

Polarized Raman Spectra II. Anthracene Crystal

The polarized Raman spectrum in crystalline anthracene is recorded using an Ar⁺ laser as the light source. With the polarization data, empirical criteria of assigning molecular vibrations to A_g and B_sg representations are derived. These criteria are discussed in the light of the theory developed in Part I of this series.¹ The lack of vibrational exciton structures in the spectrum of anthracene crystal is the strongest evidence to discredit the conventional polarizability theory and to support the theory presented in Part I. The assignments of 11 A_g and 9 B_sg vibrations in anthracene-h₁₀, and also 12 A_g and 7 B_sg vibrations in anthracene-d₁₀ are reported.     

Vibrational dephasing and hydrodynamic effects on vibrational relaxation rates in acetophenone: Raman bandshape analysis

The isotropic component of Raman band for C=O stretching mode of acetophenone in solution was analyzed by estimating the correlation coefficient with reference to Lorentzian lineshape. In the intermediate region of solute/solvent concentration there is a sharp decrease in the correlation coefficient and there appears to be a transition from non-Lorentzian to Lorentzian lineshape. The vibrational relaxation rates have been estimated from the isotropic component of Raman band in different solvents. The rate is shown to be dependent on several macroscopic as well as microscopic properties of the solute-solvent system and intermolecular interactions. The hydrodynamic and dispersion forces appear to play a major role in determining the vibrational relaxation rate and the broadening of the bands.     

Alkali metal intercalated titanate nanotubes: A vibrational spectroscopy study

Alkali metal (Li⁺, Na⁺, K⁺) intercalated titanate nanotubes have been studied by vibrational spectroscopy (Raman and FT-infrared), X-ray diffraction, and electron microscopy. The vibrational spectroscopic data shown that the most affected vibrational mode is that related to Ti-O bond whose oxygen is not shared among the TiO₆ units of the framework structure. A correlation between vibrational frequency shifts and intercalated metal was found, thus showing that vibrational spectroscopy is very useful for probing metal intercalated titanate nanotubes. Our results provide good evidences that the structure of titanate layers in titanate nanotube, a subject of long debate in the literature, is similar to trititanates (like Na₂Ti₃O₇).     

High pressure raman study of isotropic lineshapes of aqueous sodium nitrate solutions

The isotropic lineshape of the v₁ (A₁) stretching mode of the nitrate ion in solutions of sodium nitrate has been studied at 25°C as a function of NaNO₃ concentration ranging from 0.1 to 6M. The pressure dependence has been determined for 1 and 6M solutions at pressures ranging from 1 bar to 3 kbar. The isotropic band becomes more asymmetric with increasing concentration, and its v₁ peak frequency undergoes a blue shift both with increased concentration and increased pressure. At low concentration the vibrational correlation function is well described by the Kubo formula, whereas at higher concentration it becomes more Gaussian. The experimental data indicate that the v₁ vibrational lineshape in aqueous solutions of NaNO₃ is dominated by strong intermolecular interactions which produce inhomogeneous broadening at higher concentration.     

Comparison of the Electronic and Vibrational Optical Activity of a Europium(III) Complex

The geometry and the electronic structure of chiral lanthanide(III) complexes are traditionally probed by electronic methods, such as circularly polarised luminescence (CPL) and electronic circular dichroism (ECD) spectroscopy. The vibrational phenomena are much weaker. In the present study, however, significant enhancements of vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectral intensities were observed during the formation of a chiral bipyridine–Eu^III complex. The ten‐fold enhancement of the vibrational absorption and VCD intensities was explained by a charge‐transfer process and the dominant effect of the nitrate ion on the spectra. A much larger enhancement of the ROA and Raman intensities and a hundred‐fold increase of the circular intensity difference (CID) ratio were explained by the resonance of the λ=532 nm laser light with the ⁷F₀ → ⁵D₀ transitions. This phenomenon is combined with a chirality transfer, and mixing of the Raman and luminescence effects involving low‐energy ⁷F states of europium. The results thus indicate that the vibrational optical activity (VOA) may be a very sensitive tool for chirality detection and probing of the electronic structure of Eu^III and other coordination compounds.     

亮氨酸与异亮氨酸的表面增强拉曼光谱

报道了在蛋白质氨基酸中唯一一对异构体氨基酸——亮氨酸和异亮氨酸的FT-拉曼光谱和在银胶基底上的表面增强拉曼光谱(SERS). 归属了各振动、增强峰位并分析了异构体氨基酸分子内不同振动模式引起的拉曼位移及其在不同pH值下SERS的变化. 分子内不同的振动模式主要源于异构体氨基酸中一个甲基和主链的不同连接次序, 表现在拉曼光谱; 亮氨酸的甲基摇摆ρ(CH₃)和非对称变形δ_as(CH₃)在962, 945, 924和1454, 1408 cm^－1; 异亮氨酸的ρ(CH₃), δ_as(CH₃)在922和1448, 1420, 1394 cm^－1. C—CO, C—C, H—O…H及骨架晶格振动峰位基本对应. 饱和液态的拉曼光谱和SERS中, 各基团振动峰位的差异表现得更为明显. 初步推测了这对氨基酸异构体在银表面吸附状态的模型.     

Raman spectroscopy in liquids at high pressure

The pressure dependence of the reorientational correlation function for chloroform has been measured by analysis of the Raman 3019 cm^{? 1} A₁ CH stretching lineshape at 1, 1000, and 2000 bar and 23°C. These reorientational correlation functions were obtained using the method of spectral Fourier deconvolution introduced by Bratos. The results are compared to the correlation times obtained from the NMR deuteron T₁ relaxation times for CDCl₃ and those calculated from high pressure viscosity measurements.     

Schwingungsspektren und strukturchemie von heterometall-komplexen und -clustern mit thiometallat-liganden

The thioanions of the early transition metals, e.g. MoOS₃^2?, WOS₃^2?, MoS₄^2? and WS₄^2?, form hetero-metal complexes, which are interesting because of their electronic properties and their relevance to problems of bioinorganic chemistry. Their vibrational spectra are discussed in relation to the molecular structure of the compounds and especially to the wide variety of the coordination types of the thiometalate ligands. It is demonstrated that vibrational spectroscopy (especially Raman and resonance Raman) is a powerful tool for the determination of the local symmetry of the thioanions in polynuclear coordination compounds.     

Spectroscopic studies of the conformations of n-decamethyltetrasilane

The conformational properties of n-decamethyltetrasilane, n-Si₄(CH₃)₁₀, have been studied by variable temperature NMR (¹H and ¹³C) and vibrational (IR and Raman) spectroscopy. As in related alkane systems, the anti conformer ismore stable than the gauche conformer. Values of △H⁰ and △S⁰ for the anti → gauche reaction are 2.26 ± 0.15 kJ mol^-1 and △S⁰ = 7.82± 0.86 J K^-1mol^-1, respectively. Thus, the two conformers are present in comparable quantities at room temperature. At very low temperatures, broadening of the two proton resonances (SiMe₂, SiMe₃) occurs, but phase changes precluded the observation of decoalescence. By approximate lineshape anaylysis, the free energy of activation, △G3, for rotation about the central SiSi bond is estimated to be ～25 kJ mol^-1.     

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.