DFT studies on the vibrational and electronic spectra of acetylsalicylic acid

The following is a theoretical and experimental study on the vibrational and electronic properties of acetylsalicylic acid (ASA). Vibrational information was obtained by FT-IR and Raman spectroscopy which agree well with harmonic vibrational frequency calculations. The calculations were carried out using density functional theory B3LYP methods with 6-311G** and LANL2DZ basis sets. The vibrational assignments were calculated by Gaussview. Absorption UV-Vis experiments of ASA reveal three maximum peaks at 203, 224 and 277 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311G**.     

The electronic structure and spectra of octacyanide complexes

The optical and electron spin resonance spectra of molybdenum and tungsten octacyanides have been measured and the results are interpreted by electrostatic crystal field theory using a point charge model of D _2d symmetry.     

Characteristic features of electronic and vibrational spectra of free polyatomic molecules

The functional relationships between the basic characteristics of individual bands of electronic and vibrational spectra of free polyatomic molecules are ascertained. These basic characteristics are the position of the maximum of an individual electronic-vibrational band, the rate of the temperature shift of the maximum of a band, the half-width of a homogeneously or heterogeneously broadened electronic-vibrational band, the rate of the temperature variation of the half-width of a band, the asymmetry parameter of a heterogeneously broadened band, and the conditions for symmetric or asymmetric distribution of the intensity over the contour of a spectral band. The interrelations between the basic spectral characteristics result from the sequential mechanism of formation and broadening of individual bands of electronic and vibrational spectra of free polyatomic molecules. It is shown that the investigation of the basic spectral characteristics of electronic-vibrational bands and their interrelations allows one to elucidate the nature of the internal motion determining the optical properties of polyatomic molecules.     

On the mechanism of the broadening of the proton vibrational IR band in weak hydrogen bonds. Double adiabatic approximation

It is proposed that broadening of the ν_s (AH) IR band is due to the ν_s (AH) and ν_σ (AH…B) mode coupling and to the stochastic variation of the equilibrium distance R_e (A…B) modulating the proton vibration. The R_e disordering variation is caused by a coupling of the ν_σ mode with the low frequency oscillators (ν_Q) of the medium and of the complex as such. Besides, the (ν_σ, ν_Q) and (ν_s, ν_σ) couplings cause a ν_s frequency shift. Both the band broadening and the frequency shift increase with higher force constants responsible for (ν_σ, ν_Q) mode coupling. Furthermore the Q_i low frequency stochastic vibrations directly modulate the ν_σ (AH…B) vibration and the free AH groups stretching vibration (ν^o_s) causing some broadening at their bands which is however several times smaller than the ν_s band broadening in the complex. Several examples are reported to confirm the proposed model.     

Shift and broadening of the vibrational mode for a diatomic molecule adsorbed on a metal surface

The shift and broadening of the vibrational frequency of a diatomic molecule adsorbed on a metal surface are calculated on the basis of electromagnetic interactions. Finite molecular size and nonlocal metal response are included in a calculation of the response function, whose pole is the complex normal mode frequency. Finite molecular size is described by a model of a point-like vibrational mode within a polarizable sphere. Nonlocal metal response is described by a semiclassical infinite barrier model with a Lindhard dielectric constant generalized to include core polarization and finite electron lifetime. When applied to the case of CO adsorbed on Cu and if the molecule is positioned so as to fit the observed width, it is found the predicted shift is a factor of three or more greater than that observed.     

取代基对8-羟基喹啉金属配合物电子光谱和二阶非线性光学性质的影响

在B3LYP/LANL2DZ/6-31G^*水平上优化目标化合物分子的几何结构,并分别在TD- B3LYP/LANL2DZ/6-31++G^**和B3LYP/LANL2DZ/6-31++G^**水平计算目标化合物分子的电子吸收光谱和二阶非线性光学性质.计算结果表明,引入共轭给电子基使配合物分子的最大吸收波长红移,强共轭吸电子基的引入使配合物的最大吸收波长蓝移,取代基的引入使IrQ₃型配合物的二阶非线性光学性质明显增大.对AgQ型配合物,电子跃迁属于配体内部的电荷转移（LLCT）.对PtQ₂和IrQ₃型配合物,电子跃迁属于LLCT和部分金属向配体的电荷转移.取代基对AgQ,PtQ₂,IrQ₃型配合物分子的跃迁性质几乎无影响. 关键词： 8-羟基喹啉金属配合物 电子光谱 二阶非线性光学性质 密度泛函理论     

Shift and broadening of adsorbate vibrational modes

The shift and broadening of the vibrational frequency of the adsorbate on a metal surface are calculated on the basis of two different models. The first model is an anharmonic one which includes multiphonon processes to all order in first-order perturbation theory. We show that anharmonic damping due to multiphonon processes is substantial for CO adsorbed on a Ni(100) surface and small for H adsorbed on a W(100) surface. At room temperature multiphonon processes with n > 2 are very important even in cases when the frequency of vibration of the adsorbate lies below twice the maximum phonon frequency of the substrate (n is the order of the process). For the CNi stretching mode of top-bonded CO on Ni(100) our results are in accord with the experimental data. The second model is an electronic one which includes the electron-hole pair loss mechanism. We show that the observed shift and broadening of the CO stretching vibration mode for a CO molecule adsorbed on Cu(100) and for a H atom adsorbed on a W(100) surface can be explained on the basis of this model. Variation of the shift and broadening of the CO stretching mode with the distance from a CO molecule to Ni(111) surface are calculated.     

Accurate vibrational energy spectra and dissociation energies of some diatomic electronic states

An algebraic method (AM) used to study the full vibrational spectra of diatomic systems, and an analytical formula used to calculate accurate molecular dissociation energies are applied to study the full vibrational spectra and molecular dissociation energies of some electronic states of homonuclear and heteronuclear diatomic molecules and diatomic ions. Studies show that the AM method and the analytical expression are reliable and economical physical methods for studying full vibrational spectra and molecular dissociation energies of diatomic electronic systems theoretically. They are particularly useful for those diatomic systems whose highlying vibrational energies may not be available.     

Accurate vibrational energy spectra and dissociation energies of some diatomic electronic states

An algebraic method (AM) used to study the full vibrational spectra of diatomic systems, and an analytical formula used to calculate accurate molecular dissociation energies are applied to study the full vibrational spectra and molecular dissociation energies of some electronic states of homonuclear and heteronuclear diatomic molecules and diatomic ions. Studies show that the AM method and the analytical expression are reliable and economical physical methods for studying full vibrational spectra and molecular dissociation energies of diatomic electronic systems theoretically. They are particularly useful for those diatomic systems whose high-lying vibrational energies may not be available.      

On dip broadening in transmission spectra of synthetic opals

This paper reports on a comprehensive immersion spectroscopy study of the spectral position and profile of the dip corresponding to the (111) photonic band in the transmission spectra of synthetic opals. The variation in the opal-filler permittivity contrast in the region of the immersion-mediated disappearance of the (111) band has revealed its anomalous abrupt behavior. The width of the (111) photonic band at the L point of the Brillouin zone of the fcc lattice has been calculated as a function of the opal-filler permittivity contrast in the plane wave approximation. The experimentally observed (111) dip width is found to be substantially larger than that obtained in the calculations, which can be due to deviations in the size and dielectric parameters of the a-SiO₂ particles making up synthetic opals.     

The vibrational structure of the electronic spectra of quinoxaline in shpolskii-type hydrocarbon matrices

Quasilinear spectrum of the S₁(n, π¹, ¹B₁) ← S₀ transition of quinoxaline in crystalline methylcyclohexane matrix and quasilinear phosphorescence spectra of quinoxaline in high- and low-temperature modifications of isooctane matrix were obtained at 77 K. The results of a full vibrational analysis of the spectra are presented and discussed. The diffuseness of the absorption spectrum in the range 3200-2900 Å is ascribed essentially to a small energy gap between the S₂ and S₃ states. The activity of out-of-plane vibration, 865 cm^-1, in the phosphorescence and the influence of matrices on the structure of the spectra suggest the possibility of out-of-plane distortion of the quinoxaline molecule in the T₁ state.     

On the XPS spectra of some carbonyl complexes and the effective charge of the metal and ligand atoms

X-ray photoelectron spectra have been recorded for a series of anionic carbonyl complexes, i.e., M(CO)₅X⁻, M = Cr, Mo; X = Cl, Br. The data are used to calculate the atomic charges in the complexes, using previously determined relations between binding energies and charges. As the binding energies for O1s were found to be sensitive to the degree of backbonding, probably because of extensive relaxation, the oxygen charges could only be estimated indirectly, from the condition that the total anionic charge was −1 a.u.