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Molecular structure and vibrational spectra of methyl cyanoacetate: an FT-IR, raman and ab initio molecular orbital study

Neta, João Miguel F.; Fausto, Rui
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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36.15%
The results of a combined vibrational and structural study of methyl cyanoacetate undertaken by Raman and infrared spectroscopy, and ab initio SCF-MO calculations are presented. It is shown that for the isolated molecule situation, as well as in the liquid phase, methyl cyanoacetate exists as a mixture of two main conformers of similar energies, differing by the relative orientation of the NC---C---C=O axis (the syn and skew forms, having a NC---C---C=O dihedral angle equal to 0° and in the ± 140° region, respectively). In the crystalline state, only the thermodynamically most stable syn conformer remains. The ab initio SCF-MO optimized geometries of the various possible conformers, their relative stabilities, dipole moments and harmonic force-fields are presented, and the conformational dependence of some relevant structural parameters is used to characterise the most important intramolecular interactions present in the various forms studied. Finally, results of a normal mode analysis based on the ab initio calculated vibrational spectra are used to help interpret the experimental vibrational data, enabling a detailed assignment of both Raman and infrared spectra.; http://www.sciencedirect.com/science/article/B6TGS-3SR3BN2-5/1/852e4ebf0672b59086f751b298a511ae

Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations

Alves, Horacio Wagner Leite; SILVA, C. C.; Lino, Antonio Tadeu; Borges, Pablo Damasceno; Scolfaro, Luísa Maria Ribeiro; Silva Junior, Eronides Felisberto da
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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We present our theoretical results for the structural, electronic, vibrational and optical properties of MO(2) (M = Sn, Zr, Hf and Ti) obtained by first-principles calculations. Relativistic effects are demonstrated to be important for a realistic description of the detailed structure of the electronic frequency-dependent dielectric function, as well as of the carrier effective masses. Based on our results, we found that the main contribution of the high values calculated for the oxides dielectric constants arises from the vibrational properties of these oxides, and the vibrational static dielectric constant values diminish with increasing pressure. (c) 2008 Elsevier B.V. All rights reserved.

Molecular Ordering in Layer-by-Layer Polyelectrolyte Films Studied by Sum-Frequency Vibrational Spectroscopy: The Effects of Drying Procedures

SILVA, Heurison S.; UEHARA, Thiers M.; BERGAMASKI, Kleber; MIRANDA, Paulo Barbeitas
Fonte: AMER SCIENTIFIC PUBLISHERS Publicador: AMER SCIENTIFIC PUBLISHERS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.01%
Sum-Frequency Vibrational Spectroscopy (SFVS) has been used to investigate the effect of nitrogen-flow drying on the molecular ordering of Layer-by-Layer (LbL) films of poly(allylamine hydrochloride) (PAH) alternated with poly(styrene sulfonate) (PSS). We find that films dried by spontaneous water evaporation are more ordered and homogeneous than films dried by nitrogen flow. The latter are quite inhomogeneous and may have regions with highly disordered polymer conformation. We propose that drying by spontaneous water evaporation reduces the effect of drag by the drying front, while during nitrogen-flow drying the fast evaporation of water ""freezes"" the disordered conformation of adsorbed polyelectrolyte molecules. These findings are important for many applications of LbL films, since device performance usually depends on film morphology and its molecular structure.; FINEP (Brazil); Financiadora de Estudos e Projetos (FINEP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Capes; Universidade de São Paulo (USP); Universidade de São Paulo USP; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Vibrational properties, crystal X-ray diffraction structure and quantum chemical calculations on a divalent sulfur substituted phthalimide: 1H-Isoindole-1,3(2H)-dione, 2-[(methoxycarbonyl)thio]

TORRICO-VALLEJOS, Sonia; ERBEN, Mauricio F.; PIRO, Oscar E.; CASTELLANO, Eduardo Ernesto; VEDOVA, Carlos O. Della
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Structural and conformational properties of 1H-Isoindole-1,3(2H)-dione, 2-[(methoxycarbonyl)thio] (S-phthalimido O-methyl thiocarbonate) are analyzed using a combined approach including X-ray diffraction, vibrational spectra and theoretical calculation methods. The vibrational properties have been studied by infrared and Raman spectroscopies along with quantum chemical calculations (B3LYP and B3PW91 functional in connection with the 6-311++G** and aug-cc-pVDZ basis sets). The crystal structure was determined by X-ray diffraction methods. The substance crystallizes in the monoclinic P2(1)/c space group with a = 6.795(1), b = 5.109(1), c = 30.011(3) angstrom, beta = 90.310(3)degrees and Z = 4 molecules per unit cell. The conformation adopted by the N-S-C=O group is syn (C=O double bond in synperiplanar orientation with respect to the N-S single bond). The experimental molecular structure is well reproduced by the MP2/aug-cc-pVDZ method. (C) 2010 Elsevier B.V. All rights reserved.; Facultad de Ciencias Exactas, Universidad Nacional de La Plata; Facultad de Ciencias Exactas, Universidad Nacional de La Plata; Deutscher Akademischer Austauschdienst (DAAD); DAAD

Espectroscopia vibracional e eletrônica de Diaminoantraquinonas como sondas de microambientes; Vibrational and electronic spectroscopy of diaminoanthraquinones as microenvironment probes

Lopes, José Guilherme da Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/03/2007 PT
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No presente trabalho utilizamos as espectroscopias eletrônica e vibracional, com o apoio de simulação computacional de líquidos para estudar o comportamento solvatocrômico e ionocrômico de diaminoantraquinonas. Adicionalmente estudamos a potencialidade da 1,2-diaminoantraquinona (1,2-DAAQ) no reconhecimento de ânions em superfícies de prata. Utilizando espectroscopia de absorção obtivemos espectros da 1,2-DAAQ e alguns isômeros em diversos solventes. Estes resultados foram analisados por métodos empíricos de solvatocromismo, principalmente, pela escala solvatocrômica de Kamlet-Taft. Esta análise nos propiciou um conhecimento preciso sobre o comportamento da 1,2-DAAQ em meio solvente e serviu de suporte para o estudo do ionocromismo, e da interação com as superfícies. Através da simulação computacional geramos estruturas de soluções da 1,2-DAAQ em três solventes e analisamos a estrutura destas soluções via análise das Funções de Distribuição Radial de pares, o que nos possibilitou uma visão no nível microscópico do efeito das interações com o solvente. As estruturas geradas serviram de base para o cálculo do espectro de absorção para comparação com os valores experimentais. Baseado nesta comparação foi possível especular que a estrutura da 1...

Propriedades vibracionais de defeitos de nitrogênio em nanotubos de carbono; Vibrational Properties of Nitrogen Defects on Carbon Nanotubes

Silva, Leandro de Andrade
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/11/2008 PT
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O trabalho anteriormente realizado pelo nosso grupo, onde foram simulados defeitos de nitrogênio em nanotubos de carbono, apresentou resultados interessantes relativos às energias e propriedades eletrônicas. A interpretacão dos resultados teóricos obtidos levou à proposta da Divacância rodeada por 4 Nitrogênios como estrutura mais estável para o nitrogênio tipo piridina, em constraste com aquela proposta pelos experimentais, uma Monovacância rodeada por 3 Nitrogênios. Os cálculos das propriedades eletrônicas da Divacância reproduziram as medidas experimentais na investigação de sensores de amônia. Dessa forma, como informação adicional na determinaçã da estrutura mais estável, o presente trabalho investigou as propriedades vibracionais daqueles sistemas que apresentaram menor energias de formação. Foram calculadas as freqüências vibracionais dos seguintes três defeitos: Nitrogênio Substitucional (1N), Monovacância rodeada por 3 Nitrogênios (3NV) e Divacância rodeada por 4 Nitrogênios (4ND) e comparadas com os resultados para os tubos puros. Utilizou-se a aproximação de supercélula, com 140 átomos para um tubo metálico (5,5) e 160 para um tubo semicondutor (8,0). Como o objetivo é identificar as características de cada sistema...

Basis sets applied to the theoretical study of the vibrational structure of hexaaquaaluminum(III) ion

Treu, O.; Pinheiro, J. C.; Kondo, R. T.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 109-112
ENG
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Gaussian basis sets were developed with the Generator Coordinate Hartree-Fock (GCHF) method for the atoms from H (14s), O (23s16p), and Al (29sl9p) in the ground state. These basis sets were then contracted to 3s (12,1,1), 5s3p (18,2,1,1,1/14,1,1), and 7s5p (20,3,2,1,1,1,1/14,2,1,1,1) for H, O and Al atoms, respectively, by a standard procedure. The quality of contracted basis sets in molecular calculations was evaluated through studies of the total and orbital (epsilon(HOMO) and epsilon(HOMO-1)) energies at the HF level for the hexaaquaaluminum(III) ion, [AI(H(2)O)(6)](3+). For the O atom, the 5s3p was supplemented with d polarization function and it was used in combination with 3s, and 7s5p for H and Al atoms was used to the theoretical interpretation of the Infrared (IR) spectrum of hexaaquaaluminum(III) ion. The calculations of the IR-spectrum were also performed at the HF level and it showed that the basis sets obtained with the aid of GCHF method lead to the selection of useful contracted Gaussian basis sets for the theoretical study of vibrational property of ionic specie of our interest. (C) 2004 Elsevier B.V. All rights reserved.

Direct vibrational structure of protein metal-binding sites from near-infrared Yb3+ vibronic side band spectroscopy.

Roselli, C; Boussac, A; Mattioli, T A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 20/12/1994 EN
Relevância na Pesquisa
36.15%
Near-infrared Yb3+ vibronic side band (VSB) spectroscopy is used to obtain structural information of metal binding sites in metalloproteins. This technique provides a selective "IR-like" vibrational spectrum of those ligands chelated to the Yb3+ ion. VSB spectra of various model complexes of Yb3+ representing different ligand types were studied to provide references for the VSB spectra of Yb(3+)-reconstituted metalloproteins. Ca2+ in the calcium-binding protein parvalbumin and Fe3+ in the iron-transporting protein transferrin were replaced with Yb3+. The fluorescence of Yb3+ reconstituted into these two proteins exhibits weak VSBs whose energy shifts, with respect to the main 2F5/2-->2F7/2 Yb3+ electronic transition, represent the vibrational frequencies of the Yb3+ ligands. The chemical nature of the ligands of the Yb3+ in these proteins, as deduced by the observed VSB frequencies, is entirely in agreement with their known crystal structures. For transferrin, replacement of the 12CO3(2-) metal counterion with 13CO3(2-) yielded the expected isotopic shift for the VSBs corresponding to the carbonate vibrational modes. This technique demonstrates enormous potential in elucidating the localized structure of metal binding sites in proteins.

Water dynamics in small reverse micelles in two solvents: Two-dimensional infrared vibrational echoes with two-dimensional background subtraction

Fenn, Emily E.; Wong, Daryl B.; Fayer, M. D.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.14%
Water dynamics as reflected by the spectral diffusion of the water hydroxyl stretch were measured in w0 = 2 (1.7 nm diameter) Aerosol-OT (AOT)∕water reverse micelles in carbon tetrachloride and in isooctane solvents using ultrafast 2D IR vibrational echo spectroscopy. Orientational relaxation and population relaxation are observed for w0 = 2, 4, and 7.5 in both solvents using IR pump–probe measurements. It is found that the pump–probe observables are sensitive to w0, but not to the solvent. However, initial analysis of the vibrational echo data from the water nanopool in the reverse micelles in the isooctane solvent seems to yield different dynamics than the CCl4 system in spite of the fact that the spectra, vibrational lifetimes, and orientational relaxation are the same in the two systems. It is found that there are beat patterns in the interferograms with isooctane as the solvent. The beats are observed from a signal generated by the AOT∕isooctane system even when there is no water in the system. A beat subtraction data processing procedure does a reasonable job of removing the distortions in the isooctane data, showing that the reverse micelle dynamics are the same within experimental error regardless of whether isooctane or carbon tetrachloride is used as the organic phase. Two time scales are observed in the vibrational echo data...

The promoting vibration in human heart lactate dehydrogenase is a preferred vibrational channel

Davarifar, Ardy; Antoniou, Dimitri; Schwartz, Steven D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.13%
We examine if the rate promoting vibration of lactate dehydrogenase is a preferred axis of thermal energy transfer. While it seems plausible that such a mechanistically important motion is also a favored direction of energy transfer, none of the previous studies of rate promoting vibrations in enzymatic catalysis have addressed this question. It is equally likely that the promoting vibration, though catalytically important, has no different properties than any other axis in the protein. Resolution of this issue is important for two reasons: First, if energy is transferred along this axis in a preferred fashion, it shows that the protein is engineered in a way that transfers thermal energy into a motion that is coupled to the chemical step. Second, the discovery of a preferred direction of thermal transfer provides a potential route to experimental verification of the promoting vibration concept. Our computational experiments are specifically designed to mimic potential laser experiment with the deposition of thermal energy in an active site chromophore with subsequent measurement of temperature at various points in the protein. Our results indicate that the promoting vibration is indeed a preferred channel of energy transfer. In addition...

The structure of model membranes studied by vibrational sum frequency spectroscopy

Liljeblad, J.F.D.; Rutland, M.W.; Bulone, V.; Johnson, C.M.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Conference paper
Publicado em //2010 EN
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The structure and order of insoluble Langmuir monolayers consisting of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC or 18:0 PC) and the surrounding water molecules have been investigated by vibrational sum frequency spectroscopy (VSFS). At surface pressures of 1, 15, and 57 mN/m corresponding to molecular areas of 53, 50, and 43 Å2, respectively, the DSPC molecules formed a well ordered film. Both the VSF signal from the methyl stretching vibrations of the lipid and the surrounding water increased with enhanced surface pressure, as a result of the higher surface density and increased order of the system. Water molecules hydrating the polar parts of the headgroup and in close contact to the hydrocarbon groups of the lipid were observed in all three polarization combinations of the laser beams, and distinguished by their different vibrational frequencies.; Jonathan F. D. Liljeblad, Mark W. Rutland, Vincent Bulone, C. Magnus Johnson

Structure, stability, depolarized light scattering, and vibrational spectra of fullerenols from all-electron density-functional-theory calculations

RIVELINO, Roberto; MALASPINA, Thaciana; FILETI, Eudes E.
Fonte: AMER PHYSICAL SOC Publicador: AMER PHYSICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.15%
We have investigated the stability, electronic properties, Rayleigh (elastic), and Raman (inelastic) depolarization ratios, infrared and Raman absorption vibrational spectra of fullerenols [C(60)(OH)(n)] with different degrees of hydroxylation by using all-electron density-functional-theory (DFT) methods. Stable arrangements of these molecules were found by means of full geometry optimizations using Becke's three-parameter exchange functional with the Lee, Yang, and Parr correlation functional. This DFT level has been combined with the 6-31G(d,p) Gaussian-type basis set, as a compromise between accuracy and capability to treat highly hydroxylated fullerenes, e.g., C(60)(OH)(36). Thus, the molecular properties of fullerenols were systematically analyzed for structures with n=1, 2, 3, 4, 8, 10, 16, 18, 24, 32, and 36. From the electronic structure analysis of these molecules, we have evidenced an important effect related to the weak chemical reactivity of a possible C(60)(OH)(24) isomer. To investigate Raman scattering and the vibrational spectra of the different fullerenols, frequency calculations are carried out within the harmonic approximation. In this case a systematic study is only performed for n=1-4, 8, 10, 16, 18, and 24. Our results give good agreements with the expected changes in the spectral absorptions due to the hydroxylation of fullerenes.; FAPESB (Bahia); FAPESP (Sao Paulo); CNPq

Broadening of vibrational levels in X-ray absorption spectroscopy of molecular nitrogen in compound semiconductors

Petravic, Mladen; Gao, Qiang; Llewellyn, David; Deenapanray, Prakash; MacDonald, Daniel; Crotti, C
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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36.13%
We have used high-resolution near-edge X-ray absorption fine structure spectroscopy to study the N 1s → 1π* resonance of N2 trapped below the surface of several compound semiconductors. The vibrational fine structure, observed from all samples under co

The assignment of Qy(1,0) vibrational structure and Qx for chlorophyll a

Hughes, Joseph; Conlan, Brendon; Wydrzynski, Thomas; Krausz, Elmars
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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46.03%
We used non-photochemical persistent spectral hole-burning at 1.4 K to investigate the Qy(1,0) vibrational structure of Chl a in a water-soluble chlorophyll-binding protein (WSCP) which exhibits resolved structure in its broadband optical spectra. Franck-

Controlled assembly of graphene sheets and nanotubes: fabrication of suspended multi-element all-carbon vibrational structures

Tsioutsios, I.; Moser, J.; Plaza, J. A.; Bachtold, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/10/2013
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36.03%
We report on the fabrication and operation of a multi-element vibrational structure consisting of two graphene mechanical resonators coupled by a nanotube beam. The whole structure is suspended. Each graphene resonator is clamped by two metal electrodes. The structure is fabricated using a combination of electron-beam lithography and atomic-force microscopy nano-manipulation. This layout allows us to detect the mechanical vibrations electrically. The measured eigenmodes are localized in either one of the graphene resonators. The coupling due to the nanotube is studied by measuring the shift of the resonance frequency of one graphene resonator as a function of the vibration amplitude of the other resonator. Coupled graphene resonators hold promise for the study of nonlinear dynamics, the manipulation of mechanical states, and quantum non-demolition measurements.

Hyperfine, rotational, and vibrational structure of the triplet ground state of Rb molecules

Strauss, Christoph; Takekoshi, Tetsu; Lang, Florian; Winkler, Klaus; Grimm, Rudolf; Denschlag, Johannes Hecker; Tiemann, Eberhard
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.13%
We have performed high-resolution two-photon dark-state spectroscopy of an ultracold gas of Rb molecules in the triplet ground state at a magnetic field of about 1000 G. The vibrational ladder as well as the hyperfine and low-lying rotational structure is mapped out. Energy shifts in the spectrum are observed due to singlet-triplet mixing at binding energies as deep as a few hundred GHz x h. This information together with data from other sources is used to optimize the potentials of the triplet and singlet states in a coupled-channel model. We find that the hyperfine structure depends weakly on the vibrational level. This provides a possible explanation for inaccuracies in recent Feshbach resonance calculations.

Multi-phonon $\gamma$-vibrational bands in odd-mass nuclei studied by triaxial projected shell model approach

Sheikh, J. A.; Bhat, G. H.; Sun, Y.; Palit, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/04/2010
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36.09%
Inspired by the recent experimental data (Phys. Lett. B {\bf 675} (2009) 420), we extend the triaxial projected shell model approach to study the $\gamma$-band structure in odd-mass nuclei. As a first application of the new development, the $\gamma$-vibrational structure of $^{103}$Nb is investigated. It is demonstrated that the model describes the ground-state band and multi-phonon $\gamma$-vibrations quite satisfactorily, supporting the interpretation of the data as one of the few experimentally-known examples of simultaneous occurrence of one- and two-$\gamma$-phonon vibrational bands. This generalizes the well-known concept of the surface $\gamma$-oscillation in deformed nuclei built on the ground-state in even-even systems to $\gamma$-bands based on quasiparticle configurations in odd-mass systems.; Comment: 10 pages, 3 figures

Revealing Sub-Surface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy

Ashino, Makoto; Wiesendanger, Roland; Khlobystov, Andrei N.; Berber, Savas; Tomanek, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/04/2009
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36.07%
We propose to use the damping signal of an oscillating cantilever in dynamic atomic force microscopy as a noninvasive tool to study the vibrational structure of the substrate. We present atomically resolved maps of damping in carbon nanotube peapods, capable of identifying the location and packing of enclosed Dy@C82 molecules as well as local excitations of vibrational modes inside nanotubes of different diameter. We elucidate the physical origin of damping in a microscopic model and provide quantitative interpretation of the observations by calculating the vibrational spectrum and damping of Dy@C82 inside nanotubes with different diameters using ab initio total energy and molecular dynamics calculations.; Comment: 4 pages, 3 figures, to be published in Phys. Rev. Lett.

Vibrational quenching of CO2(010) by collisions with O(3P) at thermal energies: A quantum-mechanical study

Lara Castells, M. Pilar de; Hernández, Marta I.; Delgado Barrio, Gerardo; Villarreal, Pablo; López-Puertas, Manuel
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 251892 bytes; application/pdf
ENG
Relevância na Pesquisa
36.16%
10 pages, 6 figures, 1 table, 1 appendix.-- PACS nrs.: 34.50.Ez; 33.20.Tp; 33.15.Mt; 31.15.Ar.; The CO2(010)–O(3P) vibrational energy transfer (VET) efficiency is a key input to aeronomical models of the energy budget of the upper atmospheres of Earth, Venus, and Mars. This work addresses the physical mechanisms responsible for the high efficiency of the VET process at the thermal energies existing in the terrestrial upper atmosphere (150 K ≤ T ≤ 550 K). We present a quantum-mechanical study of the process within a reduced-dimensionality approach. In this model, all the particles remain along a plane and the O(3P) atom collides along the C(2v) symmetry axis of CO2, which can present bending oscillations around the linear arrangement, while the stretching C–O coordinates are kept fixed at their equilibrium values. Two kinds of scattering calculations are performed on high-quality ab initio potential energy surfaces (PESs). In the first approach, the calculations are carried out separately for each one of the three PESs correlating to O(3P). In the second approach, nonadiabatic effects induced by spin-orbit couplings (SOC) are also accounted for. The results presented here provide an explanation to some of the questions raised by the experiments and aeronomical observations. At thermal energies...

Vibrational Modes of Partly Filled Wine Glasses

Jundt, Gregor; Radu, Adrian; Fort, Emmanuel; Duda, Jan; Vach, Holger; Fletcher, Neville
Fonte: Acoustical Society of America Publicador: Acoustical Society of America
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Time-average holographic interferometry has been employed to study how the vibrational modes of a singing wine glass change when it is filled with a liquid. While the liquid clearly lowers the resonance frequencies, it does not change the vibrational mode structure in a first approximation. A more detailed analysis, however, reveals that the presence of the liquid causes the simultaneous excitation of two orthogonal modes that are well resolved for the empty glass.