Raman studies of the effect of density of the fermi resonance in CO2

The effects of density on the Fermi resonance interaction in CO₂ up to 534 amagat density was investigated. The Raman intensity of the polarized, anisotropic, and isotropic components of the 2ν₂ and ν₁ bands was determined as a function of the fluid density. By using the theory of Fermi resonance coupling the ratio of the unperturbed Raman polarizability matrix elements of the 2ν₂ and ν₁ bands was determined as a function of the fluid density. Changes in the vibrational anharmonicity, and an increasing repulsion of the vibration levels were found to decrease the effectiveness of the resonance interaction as the fluid density was increased, therefore altering the Raman intensity and frequency with changing density.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

Pre-resonance Raman effect and vibronic coupling of benzene and benzene-d6

The pre-resonance Raman effect was observed for liquid benzene and benzene-d₆. Great intensity enhancement was found for ν₁₀(e_1g), 2ν₈ and 2ν₁₄. The effect was expained in terms of vibronic couplings between the electronic states of the molecules.     

Vibrational spectra of transition metal hexafluoride crystals. II. Two-particle and mixed crystal spectra as techniques for determination of densities

In part II of this series two techniques for obtaining densities of exciton states are discussed: heavily doped crystals and two-particle overtone and combination bands. It is demonstrated through Raman spectra and calculations that (ν_i + ν₁) combination bands yield very nearly true density of states functions for ν_i in the case for which ν₁ is essentially dispersionless. The mixed crystal method for density of states determinations is compared to the combination band technique and approximate mixed crystal concentrations appropriate for such studies can be calibrated for individual bands. It is pointed out that the overtone method, whenever applicable, is both simpler and more accurate for exciton state studies. Detailed analyses of ν₁ and 2ν₁ show that the major contribution to overtone intensity comes from the second order polarizability derivative and not anharmonic contributions.     

Fermi resonances in the Raman spectra of alkali halide/BH4−

Raman spectra of a series of alkali-halide/BH^?₄ (and BD^?₄ crystals have been obtained. These spectra show some interesting examples of Fermi resonance type interactions between the stretching mode levels and overtone and combination band levels of the bending modes. Two resonances will be considered: (i) that between ν₁ and 2ν₄(A₁), and (ii) that between ν₃, 2ν₄ (F₂) and (ν₂+ν₄) (F₂).The F₂ resonance between ν₃, 2ν₄ and ν₂+ν₄ appears in the infrared spectrum and it has been studied on several occasions. However the equivalent Raman spectrum is of interest because the relative intensities of the bands are significantly different to those shown by the infrared spectrum.In the A₁ (and E) Raman spectrum of the stretching mode region there are two strong bands for each for the ¹⁰B and ¹¹B isotopes. The ν₁ would not be expected to show any ¹⁰B and ¹¹B splitting, but the observed bands are both closely resonating mixtures of ν₁ and 2ν₄(A₁). In fact the analysis shows that the stronger band has the higher proportion of 2ν₄ character, and the larger isotopic shift of the more intense band can then be seen to be reasonable.     

Raman spectroscopic study on NpO2 +–Ca2+ interaction in highly concentrated calcium chloride

Coordination circumstance of neptunyl ion in concentrated CaCl₂ solutions was analyzed by Raman spectrometry. Besides the symmetric stretch (ν₁) mode of NpO₂ ⁺ and NpO₂ ²⁺, the asymmetric stretch (ν₃) mode of NpO₂ ⁺ was found. The Raman intensity of the ν₃ mode increased with the concentration of CaCl₂ in the system. This would be attributable to the cation–cation interaction between Np(V) and Ca(II).     

Raman Spectroscopic Study of Rare Earth Chlorides in Alkali Chloride Eutectic Melts

Raman spectra of rare earth (REE: rare earth elements) trichloride (REE = Y, La, Ce, Pr, Sm, Gd, Dy, or Yb) dissolved in alkali chloride eutectic melts (LiCl‐KCl, LiCl‐RbCl, and LiCl‐CsCl) were measured at 793 K. The spectra showed polarized peaks centered around 240–270 cm^–1, which were identified as the totally symmetric stretching vibration (ν₁) of the octahedral REECl₆^3–. The ν₁ frequency increased with the polarizing power of the trivalent REE ions. The change in the ν₁ frequency was found to be larger for lighter lanthanides. This was attributable to the distortion of the O_h symmetry of REECl₆^3–.     

New analysis of the 2ν4, ν4+ν6, 2ν6, ν3+ν4, ν3+ν6, ν1, ν5, ν2+ν4, 2ν3, ν2+ν6 and ν2+ν3 bands of formaldehyde H212C16O: Line positions and intensities in the 3.5 μm spectral region

This work is mainly motivated by the atmospheric importance of formaldehyde. The 3.5 μm region is indeed commonly used for the infrared detection of this molecule in the troposphere and the line parameters which are presently available in the atmospheric databases for H₂CO are of rather poor quality in this spectral range. Using New Fourier transform spectra recorded in LPMA and in GSMA it has been possible to perform an extensive study of the 2ν₄, ν₄+ν₆, 2ν₆, ν₃+ν₄, ν₃+ν₆, ν₁, ν₅, ν₂+ν_4, 2ν₃, ν₂+ν₆ and ν₂+ν₃ bands of formaldehyde. Combining these data with previous frequency and intensity measurements for the ν₃+ν_4, ν₃+ν₆, ν₁, ν_5, ν₂+ν_4, 2ν₃ and ν₂+ν₆ bands [L.R. Brown R.H. Toth and A.S. Pine J. Mol. Spectosc. 406–428 and references therein] and an adequate theoretical model, it proved possible to reproduce rather satisfactorily the experimental data and to generate a list of line positions and intensities for the 3.5 μm region. The Hamiltonian model accounts for the various Coriolis-type resonances and anharmonic resonances which perturb the energy levels of the 4², 4¹6¹, 6², 3¹4¹, 3¹6¹, 1¹, 5¹, 2¹4¹, 3², 2¹6¹, and 2¹3¹ vibrational states. This is also the case for the line intensity calculations, which allow one to reproduce satisfactorily the line-by-line intensity measurements as well as the integrated intensities available in the literature.     

New Triterpenoid Glycosides from the Roots of Camellia oleifera Abel

Five new triterpenoid saponins, oleiferosides I–M ( 1 – 5 , resp.) were isolated from the roots of Camellia oleifera Abel . Their structures were elucidated by a combination of 1D‐ and 2D‐NMR spectroscopy, mass spectrometry, and chemical methods. All the compounds were identified as oleanane‐type saponins with sugar moieties linked to C(3) of the aglycone. In addition, cytotoxic activities of these saponins were evaluated against four human tumor cell lines (A549, B16, BEL‐7402, and MCF‐7) by using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) in vitro assay. All of the compounds showed significant cytotoxic activities against the tested cell lines.     

High-pressure FT IR measurements of crystalline methylene chloride up to 120 kbar in the diamond anvil cell

The FT IR spectra of pressure-induced crystalline CH₂Cl₂ at room temperature were measured at hydrostatic pressures up to 120 kbar in the diamond anvil cell. The pressure dependences of the internal modes (ν₃, ν₉, ν₈, and ν₂) are reported and compared with the result of Raman scattering measurements. The discontinuity of the slope (dν/dP) at ≈ 45 kbar for the ν₉ antisymmetric CCl streching mode indicates the pressure-induced second-order phase transition which seems to be triggered by the interaction between the ν₉ mode and the ν₃ symmetric CCl stretching mode.     

ℓ-Resonance effects in C2H2 near 13.7 μm. Part H: The two quantum hotbands

This article is the second part on ℓ-resonance effects on the rotation-vibration bands of acetylene observed in the ν₅ fundamental region. While the first part concentrated on the energy level analysis of the fundamental and the seven strongest hotbands originating in the ν₄ and ν₅ excited states for both major isotopes [Spectrochim. Acta 48A, 1203 (1992)], this article summarizes the results of the analysis of the hotbands 2ν₄ + ν₅ ← 2ν₄, ν₄ + 2ν₅ ← ν₄ + ν₅, and 3ν₅ ← 2ν₅ from which improved molecular constants for the 2ν₄ and three quantum energy levels were derived for the major isotope ¹²C₂H₂. The mixing levels within the excited vibrational states due to vibrational and rotational ℓ-resonance effects are discussed which lead to the identification of the strong “forbidden” Δℓ3 band, 2ν₄+ ν³₅←2ν^Oe₄ as a result of ℓ-resonance intensity perturbation.     

Resonance Raman spectrum of the complex [(C2H5)4N] AuBr4

A resonance Raman spectrum of the complex [(C₂H₅)₄N] AuBr₄ has been observed by use of 457.9 nm Ar⁺ excitation. Three progressions in the totally symmetric stretching fundamental ν₁ (a_1g) have been observed, viz. nν₁ (as far as n = 9), ν₂ + nν₁ (as far as n = 1), and ν₄ + nν₁ (as far as n = 6). The spectroscopic constants ω₁ and x₁₁ have been determined from an analysis of the nν₁ and ν₄ + nν₁ progressions.     

Photoacoustic study of CH4(ν3) deactivation by collisions with rare gases

CH₄(ν₃) deactivation is studied in the gas phase by the photoacoustic method at 300 K. Rapid vibration-to-vibration transfer holds the adjacent levels in a quasi-equilibrium distribution. The vibrational levels can then be grouped in two sets: (ν₂, ν₄) on the one hand and (ν₃, ν₁, 2ν₂, 2ν₄, ν₂ + ν₄) on the other. By successive dilution of CH₄ in He, Ne, Ar, we determined the vibration-to-translation-rotation rate constants characterizing the deactivation of each set. The vibration-to-vibration intermolecular rate constant which connects the two sets is also obtained.     

Raman and resonance-Raman spectra of CsI/I−3

Raman and resonance-Raman spectra of the I^?₃ ion isolated within CsI crystals have been studied using 647 nm and 488 nm exciting radiation. Sample temperatures between 300 and 20 K have been used. Eleven overtones of the symmetric stretching mode (nν₁) have been observed in the resonance-Raman spectrum excited by the 488 nm Ar⁺ laser line. Bands centred at 153, 170, 264 and 304 cm^?1 have been assigned as ν₃, 2ν₂, ν₁+ν₃ and 2ν₃(Σ⁺) respectively. The remaining structure between the nν₁ lines has been assigned as due to combinations of these lines with the lattice vibrations of the CsI crystal.     

Raman analysis of SF6 molecular beams excited by a cw CO2 laser

In a molecular beam the effects of vibrational pumping of SF₆ (ν₃ = 948 cm^?1) are studied, using a line-tunable cw CO₂ laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (x_E/D ≤ 1), a thermal redistribution of the ν₃ excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm^?1. For excitation in the relatively rare collision regime (x_E/D ? 4), a structured non-thermal ν₁ Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν₃ mode. The value of T_rot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν₃(948 cm^?1)+ΔE_rot → h(ν₄ + ν₆)(962 cm^?1) relative to the near-resonant transfer rate (hν₃ + hν₃ → 2hν₃ + 3.5 cm^?1)].     

Resonance Raman Spectroscopic and Theoretical Study of Geometry Distortion of Thiourea in 21A State

The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile so-lution. B3LYP/6-311++G(3df,3pd) and RCIS/6-311++G(3df,3pd) calculations were done to elucidate the ultraviolet electronic transitions, the distorted geometry structure and the saddle point of thiourea in 2¹A excited state, respectively. The resonance Raman spectra were assigned. The absorption spectrum and resonance Raman intensities were modeled using Heller's time-dependent wavepacket approach to resonance Raman scattering. The re-sults indicate that largest change in the displacement takes place with the C=S stretch mode ν₆ (|△|=0.95) and noticeable changes appear in the H₅N₃H₆+H₈N₄H₇ wag ν₅ (|△|=0.19), NCN symmetric stretch+C=S stretch+N₃H₆+H₈N₄ wag ν₄ (|△|=0.18), while the moderate intensities of 2ν₁₅ and 4ν₁₅ are mostly due to the large excited state frequency changes of ν₁₅, but not due to its significant change in the normal mode displacement. The mechanism of the appearance of even overtones of the S=CN₂ out of plane deformation is explored. The results indicate that a Franck-Condon region saddle point is the driving force for the quadric phonon mechanism within the standard A-term of resonance Raman scattering, which leads to the pyramidalization of the carbon center and the geometry distortion of thiourea molecule in 2¹A excited state.     

Triterpenoids from the Roots of Camellia oleifera C.Abel and Their Cytotoxic Activities

Three new triterpenoids, 21β,22α‐diangeloyloxy‐3β,15α,16α,28‐tetrahydroxyolean‐12‐en‐23‐al ( 1 ), 21β‐angeloyloxy‐3β,15α,16α,28‐tetrahydroxy‐22α‐(2‐methylbutanoyloxy)olean‐12‐en‐23‐al ( 2 ), and 21β‐angeloyloxy‐3β,16α,28‐trihydroxy‐22α‐(2‐methylbutanoyloxy)olean‐12‐en‐23‐al ( 3 ), along with six known triterpenoids, were isolated from the roots of Camellia oleifera C.Abel . The structures of compounds 1 – 3 were elucidated on the basis of spectroscopic analyses. Moreover, all compounds isolated were evaluated for their cytotoxic activities by MTT (=3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) assay.     

傅里叶变换红外光谱结合模式识别法快速鉴别食用油的真伪

采用傅里叶变换红外光谱(FTIR)结合簇类独立软模式识别技术(SIMCA)建立了真伪食用油的快速鉴别方法. 该方法依据FTIR 的指纹特性, 收集并分析了53 个合格食用油和13 个伪造食用油的FTIR 谱图; 通过对谱图取二阶导数和标准化处理, 主成分分析(PCA)提取特征变量; 采用SIMCA 方法分别随机选取43 个合格食用油和9 个伪食用油样品的FTIR 谱图组成训练集, 构建得到真伪食用油的SIMCA 分类模型. 该模型经过剩余10 个合格食用油和4 个伪食用油的验证, 正确识别率达到了100%. 说明FTIR 结合SIMCA 可能成为快速鉴别食用油真伪的一种新方法.     

Determination of Edible Vegetable Oil Adulterants in Sesame Oil Using 1H Nuclear Magnetic Resonance Spectroscopy

An NMR method is reported for the determination of sesamin to verify the authenticity of sesame oil. The intensity of the well-resolved H2′ sesamin signal resonating at approximately 5.95 ppm is strongly correlated with the amounts of other types of vegetable oils present in the adulterated sesame oil using the relationship, y = 4.020x + 1.516 (r ²  = 0.9967). The H2′ peak intensity of sesamin was measured for sesame oil extracted directly from the mill-sourced sesame seeds because the sesame oils purchased from local markets could be adulterated. Additionally, the oils used were obtained from the seeds native to China and the Republic of Korea, because the sesamin concentrations may vary from region to region. The proposed ¹H NMR method allows for the simple identification and determination of cheaper vegetable oils used as adulterants in sesame oil. High-performance liquid chromatography was used to confirm the validity of the results obtained by NMR.     

High-pressure Raman study of liquid and molecular crystal at room temperature. Methylene chloride

Raman spectra of liquid and crystalline CH₂Cl₂ were measured at hydrostatic pressures up to 85 kbar and at room temperature. The pressure dependences of the internal modes (ν₄, ν₃, ν₉, ν₂ and ν₁) and the two external (lattice) modes are reported; the ν₄ symmetric CCl₂ bending mode is split into two major peaks at the liquid—solid phase transition point (at 11.3 kbar), and the discontinuities of the slopes for their peak frequencies against pressure suggest a second-order phase transition at ≈ 45 kbar. The pressure data are used to test the applicability of the vibrational scaling law proposed by Zallen for a molecular crystal.