Showing papers on "Hot band published in 2003"
TL;DR: In this paper, the effects of the methyl and amino substituents on vibrational frequencies of p-methylaniline (pMA) have been investigated and the applicability limits of HF, MP2 and DFT-B3LYP methods have been discussed.
Abstract: The FT-IR and FT-Raman spectra of p-methylaniline (pMA) have been recorded. Optimized molecular structures and normal vibrations of pMA have been obtained from the HF, MP2 and DFT-B3LYP methods implementing the 6-31G* and 6-31G** basis sets. Scale factors, which bring computational frequencies in closer agreement with the experimental data, have been calculated for predominant vibrational motions of the normal modes at each level considered. All observed harmonic IR and Raman bands of pMA have been assigned in the frameworks of the calculations. The assignments have been compared each other and with the 30 benzene-like modes. The effects of the methyl and amino substituents on vibrational frequencies have been investigated. The applicability limits of HF, MP2 and DFT-B3LYP methods have been discussed. The DFT-B3LYP method has been found very promising for vibrational spectral analyses.
215 citations
TL;DR: The mode spectra of finite Coulomb clusters, confined systems of charged microspheres in a complex plasma, have been determined experimentally and the transition from finite number to crystal-like properties is observed to occur around N=12 particles.
Abstract: The mode spectra of finite Coulomb clusters, confined systems of charged microspheres in a complex plasma, have been determined experimentally. The spectral power density of all possible modes has been measured for particle numbers between N=3 and N=145 under different plasma conditions. The agreement between measured and calculated mode frequencies is found to be very good. From this, the parameters of the particle interaction, like particle charge and screening strength, have been extracted quantitatively. In addition, the particle and mode temperatures have been obtained. The modes and the particles show the same temperature and the principle of equipartitition holds for these systems. Moreover, certain modes of interest have been compared among the different clusters, as there are the breathing mode and intershell rotation as well as the lowest- and highest-frequency modes. Moreover, the mode-integrated spectrum shows two broad maxima which are explained from "shearlike" or "compressionlike" modes. From this analysis, the transition from finite number to crystal-like properties is observed to occur around N=12 particles. Finally, a model to visualize the transition from normal mode oscillations to wave dispersions in a 2D lattice has been proposed.
130 citations
TL;DR: In this article, the FT-IR and FT-Raman spectra of m-methylaniline (mMA) have been recorded and the normal vibrations of mMA have been obtained from the ab initio-HF and the DFT-B3LYP levels.
Abstract: The FT-IR and FT-Raman spectra of m-methylaniline (mMA) have been recorded. Optimized molecular structures and normal vibrations of mMA have been obtained from the ab initio-HF and the DFT-B3LYP levels. The 6-31G* basis set has been used for each level of calculations. Correction factors, which bring computational frequencies in closer agreement with the experimental data, have been calculated for predominant vibrational motions of the normal modes at each level of theory. All IR and Raman bands of mMA have been assigned in the frameworks of the calculations. The assignments have been compared each other and with the 30 benzene-like modes. The DFT-B3LYP/6-31G* calculations have been found more reliable than the ab initio-MP2/6-31G* calculations for the vibrational study of mMA.
126 citations
TL;DR: In this paper, low-energy vibrational modes have been investigated in polycrystalline biphenyl, para-terphenyl and para-quaterphenyl using THz-TDS.
101 citations
TL;DR: In this article, an isolated, perfectly reflecting, mirror illuminated by an intense laser pulse is studied and the resulting radiation pressure efficiently entangles a mirror vibrational mode with the two reflected optical sideband modes of the incident carrier beam.
Abstract: We study an isolated, perfectly reflecting, mirror illuminated by an intense laser pulse. We show that the resulting radiation pressure efficiently entangles a mirror vibrational mode with the two reflected optical sideband modes of the incident carrier beam. The entanglement of the resulting three-mode state is studied in detail and it is shown to be robust against the mirror mode temperature. We then show how this continuous-variable entanglement can be profitably used to teleport an unknown quantum state of an optical mode onto the vibrational mode of the mirror.
92 citations
TL;DR: In this paper, a nonequilibrium description of the vibrational energy relaxation of solvated flexible molecules such as small peptides in aqueous solution is outlined and several methodological developments are introduced to employ standard biomolecular molecular-dynamics program packages.
Abstract: A nonequilibrium description of the vibrational-energy relaxation of solvated flexible molecules such as small peptides in aqueous solution is outlined. Having in mind to employ standard biomolecular molecular-dynamics program packages, several methodological developments are introduced. To calculate the vibrational normal-mode energies for a system undergoing large-amplitude motion, an instantaneous normal-mode analysis is employed. To mimic the laser excitation of a given vibrational mode in its excited states, a computational scheme is proposed which allows us to calculate the nonequilibrium phase-space initial conditions for the solute and the solvent atoms. It is demonstrated that the vibrational relaxation dynamics sensitively depends on the accurate representation of the initially excited normal mode. In particular, effects of the quantum-mechanical zero-point energy contained by the initial state are investigated, thus elucidating the importance of quantum fluctuations. To study the validity and the performance of the method, the laser-induced amide I ν=1→0 energy relaxation of N-methylacetamid in D2O is considered. The vibrational energy relaxation rate obtained from the nonequilibrium simulations is in qualitative agreement with experiment, whereas a Landau–Teller-type calculation underestimates the rate considerably. The virtues and problems of the nonequilibrium description are discussed in some detail.
90 citations
TL;DR: The unusually strong resonant enhancement significantly improves sensitivity of chiral spectroscopy and allows detection of the chiral vibrational spectrum of a molecular monolayer for the first time.
Abstract: We show theoretically and experimentally that for sum-frequency vibrational spectroscopy near electronic transitions, resonant enhancement of the chiral response can be much stronger than that of the achiral response. The doubly resonant spectrum selectively enhances the vibrational modes through their different electron-vibration couplings. The unusually strong resonant enhancement significantly improves sensitivity of chiral spectroscopy and allows detection of the chiral vibrational spectrum of a molecular monolayer for the first time.
86 citations
TL;DR: In this paper, femtosecond pump-probe experiments reveal new vibrational bands of the keto-S1 state, including the carbonyl stretching band formed by hydrogen transfer.
72 citations
TL;DR: In this paper, the anharmonic dynamics of a protein molecule was studied by molecular dynamics simulations of the intramolecular vibrational energy transfer in myoglobin, where a small excess kinetic energy was added to a specified normal mode, and the process of the energy transfer to other modes was observed.
Abstract: The anharmonic dynamics of a protein molecule was studied by molecular dynamics simulations of the intramolecular vibrational energy transfer in myoglobin. A small excess kinetic energy was added to a specified normal mode, and the process of the energy transfer to other modes was observed. It was found that the vibrational energy was transferred by two distinct mechanisms depending on temperature. Near zero temperature, the vibrational energy is transferred as a process of the Fermi resonance mostly through the third-order coupling terms from one mode to only a limited number of modes, satisfying the resonance condition. As the temperature increases, the resonance-type transfer is dominated by the off-resonance energy transfer through various mode-coupling terms. Near room temperature, the energy transfer involves higher-order coupling terms and indirect processes through intermediate modes in addition to the transfers through the lower-order couplings. In the short-time limit immediately after starting ...
67 citations
TL;DR: In this article, the free-base phthalocyanine H 2 Pc and its N, N -dideuterio-derivative D 2Pc have been calculated at density functional B3LYP, RBLYP and SVWN levels using the 6-31G ∗ basis set to investigate the isotope effect in the IR spectra.
61 citations
TL;DR: In this paper, the metal-dependent nature of surface bonding was explored by using the periodic trends of the surface-enhanced Raman spectra with the density-functional theory calculation results of bond geometries, bond energies, vibrational frequencies, and the force constants.
Abstract: Pyridine adsorbed on the group-VIIIA transition metal and the coinage metal (IB) electrode surfaces is employed as a model system to explore the metal-dependent nature of surface bonding. The periodic trends of the surface-enhanced Raman spectra are interpreted with the density-functional theory calculation results of bond geometries, bond energies, vibrational frequencies, and the force constants. On the basis of the normal-mode analysis the vibrational frequency shifts of the pyridine internal modes with the total symmetry are discussed in detail from the coupling between these internal modes and the N–M bonds. We show that the spectral properties of the ring breath mode (ν1) and the ring asymmetric deformation mode (ν6a) are sensitive to the interaction between metal and pyridine molecule. Although the frequency shift of the ν1 mode is generally regarded as an indicator of the bonding strength, we find that the frequency shift of the ν6a mode has a nearly linear dependence on the force constant of the ...
TL;DR: In this article, Fourier transform microwave spectroscopy has been used to investigate vibrational excitation and relaxation of diatomic molecules produced by an electric discharge in the throat of a supersonic nozzle.
Abstract: Fourier transform microwave spectroscopy has been used to investigate vibrational excitation and relaxation of diatomic molecules produced by an electric discharge in the throat of a supersonic nozzle. Rotational transitions of SO, SiO, and SiS, in vibrational states up to v=33 for 32S16O, v=45 for 28Si16O, and v=51 for 28Si32S in their ground electronic states have been detected. The isotopic species 33S16O, 34S16O, 29Si16O, 28Si18O, 29Si32S, and 28Si34S have also been observed in highly excited vibrational states. Microwave transitions include up to v=22 for the second lowest excited electronic state b 1Σ+ of SO (∼10 510 cm−1 above ground) have also been detected. Effective vibrational temperatures have been derived for each species, and a general model is proposed to qualitatively explain the observations. Vibrational excitation is caused by inelastic collisions with the hot electrons produced in the discharge. The subsequent vibrational populations are largely determined by vibration–vibration energy transfer via molecule–molecule binary collisions. Two regions can be inferred from the data: one characterized by a temperature of around 1000 K and a second region with a temperature of several thousand degrees Kelvin. Improved Dunham coefficients and correction terms for the breakdown of the Born–Oppenheimer approximation have been determined for b 1Σ+ SO, X 1Σ+ SiO, and X 1Σ+ SiS. Nuclear spin-rotation hyperfine structure for the 29Si isotopic species of SiO and SiS has been observed in all highly excited vibrational states.
TL;DR: The laser Raman and FTIR spectra of 3-aminobenzyl alcohol have been recorded and the assignment of fundamental vibrations agrees well with the calculated frequencies.
TL;DR: In this article, the gas phase vibrational spectroscopy of BrHBr−, a prototypical strongly hydrogen-bonded species, has been studied between 6 and 17 μm (590 and 1670 cm−1) by infrared vibrational predissociation of the BrH Br−⋅Ar ion.
Abstract: The gas phase vibrational spectroscopy of BrHBr−, a prototypical strongly hydrogen-bonded species, has been studied between 6 and 17 μm (590 and 1670 cm−1) by infrared vibrational predissociation of the BrHBr−⋅Ar ion. Infrared excitation was accomplished using the output of the free electron laser for infrared experiments (FELIX). Predissociation spectra were recorded by monitoring depletion of mass-selected BrHBr−⋅Ar ions as a function of excitation wavelength. Four prominent absorption bands are observed at 733, 890, 1048, and 1201 cm−1. They are assigned to the fundamental of the hydrogenic stretching mode ν3 and a sequence of ν3+nν1 combinations (n=1–3). Additional features to the blue of these bands spaced by ∼21 cm−1 are attributed to combination bands involving motion of the Ar messenger atom. Differences in the relative intensities of the ν3+nν1 combinations bands in comparison to previous matrix experiments are rationalized on the basis of the underlying dissociation dynamics.
TL;DR: In this paper, a highly accurate potential energy function for H2CO has been developed at the CCSD(T)/cc-pVTZ level, which is generated by the modified Shepard interpolation of the local fourth-order Taylor expansions defined at three reference points, i.e., the equilibrium structure plus two symmetrically equivalent structures located in the strongly coupled region of CH symmetric (Q1) and antisymmetric stretching vibrational coordinates.
Abstract: A highly accurate potential energy function for H2CO has been developed at the CCSD(T)/cc-pVTZ level. The potential energy function is generated by the modified Shepard interpolation of the local fourth-order Taylor expansions defined at three reference points, i.e., the equilibrium structure plus two symmetrically equivalent structures located in the strongly coupled region of CH symmetric (Q1) and antisymmetric (Q5) stretching vibrational coordinates. The vibrational self-consistent field and the following vibrational configuration interaction methods have been applied to determine the fundamentals, overtones, and combination bands of H2CO. It is shown that our proposed potential energy function and a conventional quartic force field provide the different result related to the assignment of the 1151 and 113161 bands. The calculated vibrational energies are in good agreement with the corresponding experimental values, showing the mean absolute deviation of 7.7 cm−1.
TL;DR: In this article, the site-selective excitation of various vibrational modes of the lower-energy trans conformer was performed using narrowband tunable infrared (IR) radiation, and the trans→cis isomerization quantum yields for the excited modes were determined.
Abstract: Formic acid molecules are trapped in two predominant local environments (sites) when isolated in an argon matrix at 8 K. Using narrowband tunable infrared (IR) radiation, we performed site-selective excitation of various vibrational modes of the lower-energy trans conformer. For all excited modes, ranging from 7000 to 2950 cm−1, we detected site-selective isomerization to the higher-energy cis form. By measuring the IR absorption of a selected band of the cis conformer as a function of the excitation frequency, the reactive vibrational excitation (RVE) spectra were obtained. The trans→cis isomerization quantum yields for the excited modes were determined. Remarkably, very high absolute values were obtained for the quantum yield (up to 40%) at excitation energies above the reaction barrier. The efficiency of the photoinduced isomerization is essentially independent of the excited vibrational mode in a broad energy interval. Even when the excitation energy was below the reaction barrier, IR-induced rotation...
TL;DR: The absorption spectrum of pyrimidine vapor at 75 °C in the region of the first singlet−triplet transition, encompassing hot bands, has been obtained and analyzed with the aid of extensive ab initio (EOM-CCSD, CASPT2, and CIS) and density functional (B3LYP and TD-B3lyP) vibrational analyses as discussed by the authors.
Abstract: The absorption spectrum of pyrimidine vapor at 75 °C in the region of the first singlet−triplet transition, encompassing hot bands of the first singlet−singlet transition, has been obtained and analyzed with the aid of extensive ab initio (EOM-CCSD, CASPT2, and CIS) and density functional (B3LYP and TD-B3LYP) vibrational analyses. The hot bands in these spectra give information about low-frequency vibrations, several of which are vibronically active but are not particularly effective at inducing intensity. Spectra obtained at 18 °C are also reported for up to 1100 cm-1 above the singlet−singlet origin. Several singlet−singlet hot bands have been reassigned, giving excited-state vibrational frequencies for some modes. The calculations provide not only quantitative verification of perceived vibronic coupling and other features of the experimental assignments but also detailed maps of the complex lowest singlet and triplet manifolds. This includes vertical and adiabatic excitation energies, relaxation energi...
TL;DR: In this paper, a single crystal infrared (IR) reflectance spectra for the Dy3Al5O12 and Er3Al 5O12 compounds, their corresponding optical constants, as well as a discussion concerning the vibrational, dielectric, and elastic properties of various members of the rare earth aluminum garnet family are presented.
Abstract: In this work we present single crystal infrared (IR) reflectance spectra for the Dy3Al5O12 and Er3Al5O12 compounds, their corresponding optical constants, as well as a discussion concerning the vibrational, dielectric, and elastic properties of various members of the rare earth aluminum garnet family. In the framework of the rigid ion model, the frequencies of the experimentally unresolved infrared active modes, the IR eigenvectors and the partial phonon density of states have been calculated. The role of the different atomic species in the various regions of the IR vibrational spectrum has been elucidated. In particular, it is found that the rare earth ionic mass plays a crucial role in the low frequency IR modes (<200 cm−1), while the high frequency modes are related mainly to the molecular modes of the AlO4 tetrahedral subunit. From the volume dependence of the IR active mode frequencies, their mode Gruneisen parameters are estimated and discussed. Finally, by using a modification of the semiempirical ...
TL;DR: The infrared spectrum of HCN in the region between 3150 and 3450 cm −1 has been recorded at 0.005 and 0.008 cm − 1 resolution using two different Fourier transform spectrometers as mentioned in this paper.
Abstract: The infrared spectrum of HCN in the region between 3150 and 3450 cm −1 has been recorded at 0.005 and 0.008 cm −1 resolution using two different Fourier transform spectrometers, the McMath–Pierce Fourier transform spectrometer located at the National Solar Observatory (on Kitt Peak) and the Bruker-120HR Fourier transform spectrometer situated at the Pacific Northwest National Laboratory at Richland, Washington. Room temperature measurements were made of positions, absolute intensities, self-broadening and self-shift coefficients for individual lines belonging to the HCN ν1 band centered near 3311 cm −1 . These are to our knowledge the first extensive set of self-broadening and self shift measurements in the band. In addition, intensities, self-broadening and self-shift coefficients for several lines of the ν1+ν21−ν21 hot band and several intensities for lines in the H13C14N and H12C15N isotopomers were also determined. A multispectrum nonlinear least-squares fitting algorithm was used to fit the entire spectral region covering the 3200– 3400 cm −1 region of up to 27 spectra simultaneously. The measured line intensities in the ν1 band were further analyzed to derive the vibrational band intensity and the Herman–Wallis coefficients. Differences in line intensities between 5 and 10% are found with respect to present measurements and the values given in the HITRAN database for m values beyond 25 in the P branch and 5 in the R branch.
TL;DR: The vibrational energy relaxation of a selected vibrational mode in cytochrome c--a C-D stretch in the terminal methyl group of Met80-- has been studied using equilibrium molecular dynamics simulation and normal mode analysis methods.
01 Feb 2003
TL;DR: In this paper, the surface enhanced Raman scattering technique was used to analyze the low frequency vibrational modes of green fluorescent proteins (GFPs) down to 300 cm -1.
Abstract: We report the observation and analysis of the low frequency vibrational modes of green fluorescent proteins (GFPs). Our study exploits the surface enhanced Raman scattering technique, which allowed the analysis of the vibrational modes of the proteins down to 300 cm � 1 . Here we present results on two GFP mutants, namely S65T/F64L GFP (EGFP) and S65T/F64L/T203Y GFP (E 2 GFP). These particularly bright mutants display almost inverted population ratio of anionic (B) to neutral (A) forms of the chromophore. By comparing the vibrational spectrum of the proteins with that of a synthetic model chromophore in solution and with the aid of first principle calculations based on density functional theory, we identify the Raman active bands in this region of frequencies. A dominant collective mode at 720 cm � 1 is found and assigned to a collective planar deformation of the chromophore. Low frequency vibrational modes belonging specifically to A and/or Bstructural configurations are also identified. This work demonstrates the possibility of monitoring the structural sub-states of GFPs through vibrational spectroscopy in a range of frequencies where collective modes peculiar of the double ring structure of the chromophore lie. 2002 Elsevier Science B.V. All rights reserved.
TL;DR: In this article, the authors investigated ultrafast vibrational excitation and energy redistribution in the electronic ground state after internal conversion of 4-nitroaniline (PNA) and isotope labeled analogs using anti-Stokes resonance Raman spectroscopy.
Abstract: Ultrafast vibrational excitation and energy redistribution in the electronic ground state after internal conversion of 4-nitroaniline (PNA) and isotope labeled analogs is investigated by picosecond anti-Stokes resonance Raman spectroscopy. In PNA, PNA-di-15N and PNA-D4, anti-Stokes Raman lines of overtones and/or combination bands of out-of-plane vibrations display risetimes close to the decay time of the electronically excited state of about 0.5 ps and pronounced excess populations. Compared to such fast dynamics, the strongly Raman active totally-symmetric modes show a considerably slower picosecond rise time. Our results indicate primary excitation of out-of-plane vibrations by internal conversion and secondary excitation of strongly Raman active vibrations by redistribution of the vibrational energy.
TL;DR: In this article, a novel technique is demonstrated for the study of molecular vibrational dynamics in the structurally relaxed electronically excited state, where a substituted oligo (phenylene vinylene) is first optically excited and allowed to vibrationally relax.
Abstract: A novel technique is demonstrated for the study of molecular vibrational dynamics in the structurally relaxed electronically excited state. The molecule is first optically excited and allowed to vibrationally relax. During the excited-state lifetime, emission is stimulated impulsively with a resonant <10-fs pulse, inducing vibrational coherence in both coupled electronic states. These are detected by an equally short probing pulse. In this first report, the methodology is applied to a substituted oligo(phenylene vinylene) in solution, and a complex vibrational response consisting of contributions from a number of active normal modes is observed. Our analysis shows that modulations observed in the experiment result mainly from vibrational coherences in the excited electronic state. The most prominent modulation is observed at 1589 cm-1 and is assigned to the excited-state potential. The strong similarity of this frequency with that detected in resonant Raman scattering (1591 cm-1) supports electronic struc...
TL;DR: A rovibrational-state-selected photoionization experiment using an IR laser and high-resolution VUV-synchrotron radiation is demonstrated, opening the way for state-selective photoionized studies of polyatomic molecules using VUV.
Abstract: We have demonstrated a rovibrational-state-selected photoionization experiment using an IR laser and high-resolution VUV-synchrotron radiation. The VUV photoionization of acetylene [${\mathrm{C}}_{2}{\mathrm{H}}_{2}(\stackrel{\texttildelow{}}{X}\text{ }^{1}\ensuremath{\Sigma}_{g}^{+};{\ensuremath{
u}}_{3}=1,{J}^{\ensuremath{'}}=8\text{ }\mathrm{o}\mathrm{r}\text{ }10)$] prepared by IR excitation reveals three strong autoionizing Rydberg series converging to ${\mathrm{C}}_{2}\mathrm{H}_{2}{}^{+}(\stackrel{\texttildelow{}}{X}\text{ }^{2}\ensuremath{\Pi}_{u};{\ensuremath{
u}}_{3}^{+}=1)$ with little ion background interference. Rotational transitions resolved for the Rydberg states provide an estimate of $\ensuremath{\approx}1.8\text{ }\text{ }\mathrm{p}\mathrm{s}$ for their lifetimes. This experiment opens the way for state-selective photoionization studies of polyatomic molecules using VUV-synchrotron radiation.
TL;DR: In this article, the structure, bonding, electron distribution, normal mode frequencies and corresponding vibrational assignments of tetrarsenic tetrasulfide (As4S4) in D2d symmetry were examined theoretically using the gaussian 98 set of quantum chemistry codes at the HF, MP2 and B3LYP(DFT) levels of theory using the standard 6-311G* basis.
Abstract: The structure, bonding, electron distribution, normal mode frequencies and the corresponding vibrational assignments of tetrarsenic tetrasulfide (As4S4) in D2d symmetry are examined theoretically using the gaussian 98 set of quantum chemistry codes at the HF, MP2 and B3LYP(DFT) levels of theory using the standard 6-311G* basis. By comparison to experimental normal mode frequencies deduced by Chapman [Spectrochim. Acta 24A(1968)1687] correction factors for predominant vibrational motions are determined and compared. Normal modes were decomposed into four nonredundant motions {As– As stretch, As– S stretch, As–S–As bend, and As–S–As wagging modes}.
TL;DR: In this paper, high resolution Fourier transform spectra of pure 12CH335Cl and 12CH337Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm−1.
TL;DR: In this paper, a more accurate analysis of the hot band was performed using new laboratory high-resolution (0.002-0.005 cm −1 ) Fourier transform spectra, leading to a significant improvement in the simulation of atmospheric spectra.
Abstract: Nitric acid which is an important NOx atmospheric reservoir molecule exhibits a strong absorption in the 11 μm spectral region. Since this region, which corresponds to an atmospheric window, is one of the most commonly used for the retrieval of HNO3 in the atmosphere it is essential to have the best possible corresponding spectral parameters. Updates of these spectral line parameters were recently performed in the last versions of the atmospheric databases. They concern the line positions and intensities not only of the two interfering cold bands ν5 and 2ν9 but also of the ν5+ν9−ν9 hot band. This hot band exhibits indeed a sharp and strong Q branch at 885.425 cm −1 which is clearly observable in atmospheric spectra and is used for the retrievals. However, in spite of these recent updates, it proved that the spectral parameters of the ν 5 +ν 9 −ν 9 HNO 3 hot band are not accurate enough to reproduce accurately the observed atmospheric HNO3 absorption in ATMOS spectra. The present paper is dedicated to a more accurate analysis of this hot band using new laboratory high-resolution (0.002– 0.005 cm −1 ) Fourier transform spectra. As a consequence, new and more precise line positions and line intensities (about 35% weaker than in HITRAN2K) were derived leading to a significant improvement in the simulation of atmospheric spectra.
TL;DR: The normal mode frequencies and the corresponding vibrational assignments of tetraphosphorus decaoxide in tetrahedral symmetry are examined theoretically and experimentally and correction factors for predominant vibrational motions are determined and compared.
Abstract: The first complete ab initio theoretical study of tetraarsenic hexoxide (As 4 O 6 ) is reported. The normal mode frequencies, intensities and the corresponding vibrational assignments of As 4 O 6 in T d symmetry were calculated using the gaussian 98 set of quantum chemistry codes at the HF, MP2, and DFT/B3LYP levels of theory using the 6-311G* basis set. By comparison to experimental data deduced by our laboratory and others, correction factors for the calculated vibrational frequencies were determined and compared. Normal modes were decomposed into three non-redundant motions (As–O–As stretch, As–O–As bend, and As–O–As wag). Percent relative errors found for the HF, DFT, and MP2 corrected frequencies when compared to experiment are 3.6, 4.6, and 5.0, respectively. Electron distributions for selected molecular orbitals are also considered.
TL;DR: In this article, the vibrational structure of the A 1Au state has been improved by laser-induced fluorescence spectra of supersonic jet cooled acetylene (C2H2).
Abstract: New laser-induced fluorescence spectra of supersonic jet cooled acetylene (C2H2) in the wavelength region 230–205 nm have led to an improved understanding of the vibrational structure of the A 1Au state. Among the new bands observed are two weak perturbed bands at 46008 cm−1 and 46116 cm−1. Rotational analyses of these bands, together with the corresponding ‘hot’ bands arising from the ground state v4 fundamental, have shown that the upper states have asymmetric top K structure that is unaffected by a axis Coriolis coupling; this means that they do not involve overtones of the low frequency bending vibrations and therefore must be combinations of ag vibrational normal modes. From their positions in the manifold, their vibrational assignments can only be 22 031 0; and 11 0;31 0. These assignments lead to values of x 22, x13, and a revised value for the symmetric CH stretching frequency, ν1 = 2880.5cm−1; this revised value is 160cm−1 lower than the previously accepted value, but consistent with new ab initi...
TL;DR: In this paper, the rotational spectrum of HCN in excited vibrational states has been extended to higher-J values and the transitions reach J =8←7 around 710 GHz for most vibrational state studied in this investigation.