Vibrational spectroscopy of SnBr4 and CCl4 using Lie algebraic approach

The stretching and bending vibrational energies of SnBr₄ and CCl₄ are calculated in the one-dimensional framework. The dynamical symmetry group of tetrahedral molecule was taken into consideration to construct the model Hamiltonian in this framework. Casimir and Majorana invariant operators were also determined accordingly. Using the model Hamiltonian so constructed, we reported the vibrational energy levels of SnBr₄ and CCl₄ molecules accurately.      

Vibrational spectra of nickel metalloporphyrins: An algebraic approach

One of the most interesting areas of current research in molecular physics is the study of the vibrationally excitated states of medium and large molecules. In view of the considerable amount of experimental activity in this area, one needs theoretical models within which to interpret experimental data. Using Lie algebraic method, the vibrational energy levels of nickel metalloporphyrins like Ni(OEP), Ni porphyrin and Ni(TPP) are calculated for 16 vibrational modes. The algebraic Hamiltonian

Vibrational heating in single-molecule switches: an energy-dependent density-of-states approach

In recent experiments, it has been shown that the switching rate of single-molecule switches can show a rather complicated dependence on the applied bias voltage. Here, we discuss a minimal model which describes the switching process in terms of inelastic scattering processes of the tunneling electron by specific molecular vibrations. One important point is the introduction of an energy-dependent electronic density of states around the Fermi energy. The influence of different model parameters on the switching rate is studied and we show that the inclusion of a variable density of states allows us to understand the non-monotonic behavior of the switching rate observed in some experiments.     

Vibrational spectroscopy of ion-irradiated pentacene

In this paper we present a study of the evolution of the IR and Raman spectrum of pentacene before, during and after irradiation with energetic ion beams, demonstrating the complex chemistry induced by incoming ions. The formation of a “new” aromatic network has been evidenced. Dehydrogenation occurs and the evolution towards what we call an Ion Produced Hydrogenated Amorphous Carbon is a function of the ion dose as well. The results my have noteworthy relevance in astrophysics in view of the presently believed widespread presence of PAHs and their compounds in ours as well as other galaxies.     

Vibrational spectroscopy of ice interfaces

Vibrational spectroscopy via infrared-visible sum-frequency generation was used to probe interfaces of hexagonal ice(0001) with vapor, a hydrophobic solid, and a hydrophilic solid. The OH stretch vibrational modes for hydrogen-bonded and free dangling OH bonds were measured at various temperatures below bulk melting. At the vapor/ice interface, the dangling OH mode provided information about surface melting. Surface structural disordering appeared to set in at ∼200 K and increased dramatically with temperature. Received: 15 January 2002 / Published online: 11 June 2002     

Vibrational spectroscopy of articular cartilage

Articular cartilage is a connective tissue that is located at the ends of long bones. Type II collagen, proteoglycans, water, and chondrocytes are the main constituents of articular cartilage. Osteoarthritis, the most common joint disease in the world, causes degenerative changes in articular cartilage tissue. Fourier transform infrared, Raman, and near infrared spectroscopic techniques offer versatile tools to assess biochemical composition and quality of articular cartilage. These vibrational spectroscopic techniques can be used to broaden our understanding about the compositional changes during osteoarthritis, and they also hold promise in disease diagnostics. In this article, the current literature of articular cartilage spectroscopic studies is reviewed.     

Vibrational spectroscopy of interstellar molecules

In this paper we describe how infrared vibrational spectroscopy has been applied in our laboratory to three areas of interest to interstellar chemistry: the origin of the unidentified interstellar infrared emission bands, the depletion of the iron in the interstellar medium, and the fractionation of isotope-bearing molecules in space. In the first area, infrared absorption spectra of polycyclic aromatic hydrocarbons and their ions trapped in cryogenic rare gas matrices have been analyzed and shown to coincide well with the frequencies and relative intensities of the unidentified infrared emission bands. These bands have been observed from many sources in interstellar space, including reflection and planetary nebulae and H II regions, in parts of the Milky Way, as well as other galaxies. In the second area, a free electron laser, with tunable output in the infrared, has been utilized to record resonant multiphoton photodissociation vibrational spectra of various polycyclic aromatic hydrocarbons complexed with Fe⁺ in a Fourier transform ion cyclotron resonance mass spectrometer. Stable complexes found for Fe⁺ and a number of PAHs suggest that iron could be sequestered in such species and that they could function as carriers of the unidentified infrared emission bands. In the third area, the photo-induced ¹³C-isotopic scrambling in the C₃ carbon cluster has been investigated by matrix isolation infrared spectroscopy. Fractionation is shown to arise from small zero-point energy differences in the C₃ isotopomers. A proposed mechanism of isotopic scrambling involving the formation of cyclic C₃ intermediates may be applicable to other species for which isotopic fractionation has also been observed in the ISM.     

Electron impact total ionisation cross sections for simple bio-molecules: a theoretical approach

In this article, we have reported electron impact total ionisation cross sections for the bio-molecules pyridine, pyrimidine, n-propylamine, urea, formamide and N-methylformamide from ionisation threshold to 2000 eV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionisation contribution method. The results obtained for pyridine and pyrimidine are compared with available theoretical and experimental results and are found to be in excellent agreement with existing data. The ionisation cross sections for other molecules are reported for the first time. An interesting relation between the peak of inelastic and ionisation cross sections with target parameters is also reported. It was found that both the cross sections at their maximum depend linearly with these parameters, confirming the consistency of the values reported here.     

Vibrational spectroscopy of the seselin crystal

Seselin, C₁₄H₁₂O₃, is a coumarin which crystallizes in a monoclinic structure P2₁/b(C_2h⁵) with four molecules per unit cell. In a Fourier‐transform Raman spectroscopic study performed at room temperature, several normal modes were observed. Vibrational wavenumber and wave vector calculations using density functional theory were compared with experiment, which allowed the assignment of a number of normal modes of the crystal. Temperature‐dependent Raman spectra were recorded between 10 and 300 K. No anomalies were observed in the phonon spectra, indicating that the monoclinic structure remains stable. Copyright © 2007 John Wiley & Sons, Ltd.     

Unstable bound states of the Dirac equation by an algebraic approach

It is shown that by using a nonunitary discrete irreducible representation of the su(1, 1) Lie algebra one can determine the eigenenergies of unstable bound states of the Dirac-Coulomb potential. The phase shift of the Dirac-Coulomb waves is also discussed.     

Vibrational spectra of H2O and CF4 molecules using Lie algebraic approach

In this paper, we introduce one dimensional vibron model to analyze the fundamental, overtone and combination modes of CF₄ molecule and both stretching, bending vibrational mode of bent H₂O molecule up to first overtone with few algebraic parameters. Using the model Hamiltonian, we reported here better results for the vibrational spectra of H₂O. Our analysis suggests some reassignments of levels and predicts location of states in case of CF₄ molecule which was not yet observed.     

用可变阶数的代数方法研究双原子体系的完全振动能谱和离解能

不同双原子分子电子态的势能(或振动能谱)的展开性质可能不同,文章将固定阶数的代数方法(AM)改进为可变阶数的代数方法,使得该方法可以研究各种不同性质(不同能量展开阶数)的双原子分子电子态,也可以解决光谱计算中可能出现的"蝴蝶效应"问题。利用阶数可变的AM方法研究了原来固定阶数的AM方法难以给出正确结果的N2-a′1Σu-,Li2+-2 2Σg+,4 He D+-X1Σ+和39 K85 Rb-(2)3Σ+等不同双核体系的完全振动能谱与离解能,不但得到了与实验数据精确相符的理论结果,还正确地预言了许多由于实验条件与技术原因而未能测得的物理数据。研究表明阶数可变的AM方法能够更广泛地用于研究各类双核电子态体系的完全振动能谱和体系离解能。     

Vibrational spectrum of CF<Subscript>4</Subscript> isotopes in an algebraic model

In this paper the stretching vibrational modes of CF₄ isotopes are calculated up to first overtone using the one-dimensional vibron model for the first time. The model Hamiltonian so constructed seems to describe the C-F stretching modes accurately using a relatively small set of well-defined parameters.     

Vibrational spectroscopy of selective dental restorative materials

Recently, significant advancement has occurred in vibrational (Fourier transform infrared [FTIR] and Raman) spectroscopy associated with dental materials. FTIR and Raman spectroscopies have emerged as significant breakthrough techniques and offer exciting new possibilities in the area of dental materials. These techniques have been used to obtain chemical images of formulations and allow researchers to find out the in situ structure of materials. This review summarizes the information obtained from these two techniques and their application in dental material sciences. The presented database of vibrational spectroscopy facilitated the appropriate identification of frequently used dental materials ranging from filling, obturating, adhesive, lining/luting materials, and prosthodontics materials. Spectral peaks that are related to these materials are discussed in detail, which provided crucial data in understanding the chemical structural properties. The application of vibrational spectroscopy allowed for a quick differential identification of typical dental materials composed of organic and inorganic compounds. From our study as well as the literature reviewed, it appeared that investigators uniformly confirmed the benefits of vibrational spectroscopy concerning identification of chemical functional groups of different chemical compositions. The diagnostic and prognostic tools based on these technologies have the potential to revolutionize our concepts leading to improve materials sciences and clinical application.     

Vibrational spectroscopy of structural defects in oligothiophenes

Vibrational spectra of oligothiophenes with structural defects are calculated within the density-functional-theory methodology. The effects of the defective αβ linkages on the infrared (IR) and Raman spectra are characterized from calculations of all isomers up to the hexamer. The signatures of αβ linked monomers can be found in IR spectra from broken symmetry arguments which result in absorptions localized in the defective region. The positions of the absorption peaks in the Raman spectra seem to be unaffected by the presence of such defects; however, strong reductions in the intensities are observed because of the shortening of the conjugation length.