Showing papers on "Hot band published in 1995"
TL;DR: A spectroscopic method for the complete characterization of the quantum state of the vibrational mode of a molecule in terms of a phase-space quasiprobability distribution is presented.
Abstract: We present a spectroscopic method for the complete characterization of the quantum state of the vibrational mode of a molecule in terms of a phase-space quasiprobability distribution. The distribution for a molecular vibrational mode excited by a short optical pulse is reconstructed from measurements of its time-dependent spectrum of fluorescence.
238 citations
TL;DR: In this article, the vibrational population dynamics of the T1u CO stretching mode (∼1980 cm−1) of tungsten hexacarbonyl in CCl4 and CHCl3 were analyzed.
Abstract: Instantaneous normal mode calculations of the low frequency solvent modes of carbon tetrachloride (CCl4) and chloroform (CHCl3), and experiments on the vibrational population dynamics of the T1u CO stretching mode (∼1980 cm−1) of tungsten hexacarbonyl in CCl4 and CHCl3 are used to understand factors affecting the temperature dependence of the vibrational lifetime. Picosecond infrared pump–probe experiments measuring the vibrational lifetime of the T1u mode from the melting points to the boiling points of the two solvents show a dramatic solvent dependence. In CCl4, the vibrational lifetime decreases as the temperature is increased; however, in CHCl3, the vibrational lifetime actually becomes longer as the temperature is increased. The change in thermal occupation numbers of the modes in the solute/solvent systems cannot account for this difference. Changes in the density of states of the instantaneous normal modes and changes in the magnitude of the anharmonic coupling matrix elements are considered. The ...
111 citations
TL;DR: The mechanism of collisional energy transfer in collisions between a highly excited polyatomic and a monatomic bath gas is investigated for benzene-rare-gas systems by carrying out both vibrational close-coupling, infinite-order sudden quantum-scattering computations and classical trajectory calculations with a high degree of initial internal excitation as discussed by the authors.
Abstract: The mechanism of collisional energy transfer in collisions between a highly excited polyatomic and a monatomic bath gas is investigated for benzene–rare-gas systems by carrying out both vibrational close-coupling, infinite-order sudden quantum-scattering computations and classical trajectory calculations with a high degree of initial internal excitation; the quantum calculations involved up to two vibrational modes. It is found in the quantum-scattering calculations that if one of the vibrational modes is of low frequency (and particularly if it is an out-of-plane motion), then the cross-section for transferring large amounts of energy is particularly large, and involves multi-quantum transitions. Although the quantum simulations have far fewer modes (and hence involve a far lower density of states) than in an actual system, this suggests that low-frequency/out-of-plane modes are prominent in transferring significant amounts of energy (and perhaps in ‘supercollisions’), since a microcanonical ensemble in an actual system at high internal energy will contain a large proportion of states with high excitation in low-frequency modes. Both the quantum and trajectory results are consistent with a supercollision mechanism which is a head-on collision between a bath-gas atom and a rapidly moving substrate atom involved in a large-amplitude motion such as occurs with a highly excited low-frequency out-of-plane vibration.
92 citations
TL;DR: In this paper, a normal coordinate analysis of 4,4′-bipyridyl (4,4''bipy) is carried out to establish consistent vibrational assignment and to determine a Urey-Bradley force field.
70 citations
TL;DR: In this article, the rotational constants and term values for the 33 vibrational levels were determined by high-resolution (≈ 0.08 cm−1) measurements of the vibronic transitions, which were well separated from each other due to rotational and vibrational cooling.
54 citations
TL;DR: In this article, a simple vibrational Honl-London-type formula for hot-band intensities is tested by measuring the intensities of a number of vibrational transitions, including many hot bands, for HCN.
46 citations
TL;DR: In this paper, high-resolution vibrational overtone spectra of jet-cooled CH3OH, obtained using selective IRLAPS detection of the vibrational transition, reveal rich vibrational structure that carries detailed information on the intramolecular dynamics.
Abstract: Highly resolved vibrational overtone spectra of jet-cooled CH3OH, obtained using selective IRLAPS detection of the vibrational transition, reveal rich vibrational structure that carries detailed information on the intramolecular dynamics. Low-resolution single resonance spectra of the jet-cooled molecules exhibit a 50 cm–1 splitting resulting from strong coupling between the OH and CH stretch modes at the energy of the 5νOH band. Subsequent to coherent excitation, this coupling would lead to energy redistribution between the OH and CH on a 100 fs timescale. High-resolution spectra obtained using double-resonance excitation reveal smaller vibrational splittings resulting from weak vibrational couplings that control the longer time dynamics. The extensive vibrational structure in this overtone spectrum of methanol clearly indicates that it is the presence of low-order resonances rather than the total density of vibrational states that control the first 10 ps of vibrational-energy redistribution.
45 citations
44 citations
TL;DR: In this paper, the most stable molecular structures of 3-hydroxyflavone and 3-methoxy flavone have been investigated by semi-empirical calculations (AMI) at the state of isolated molecule.
44 citations
41 citations
TL;DR: In this article, the A(1B1)←X(1A1) electronic transition of difluorocarbene (CF2) has been studied by laser-induced fluorescence spectroscopy in a supersonic free jet and by ab initio theoretical methods.
Abstract: The A(1B1)←X(1A1) electronic transition of difluorocarbene (CF2) has been studied by laser‐induced fluorescence spectroscopy in a supersonic free jet and by ab initio theoretical methods. The radical was formed by pyrolysis of C2F4 at ∼1000 °C with a heating chamber at the tip of the nozzle just prior to the gas expansion. Fairly complete rotational cooling, but incomplete vibrational cooling allowed the identification of several new hot band transitions. Ab initio calculations for the X(1A1), a(3B1), and A(1B1) electronic states were performed using the CASSCF method in conjunction with Dunning’s cc‐pVTZ basis set, as well as two smaller sets. The calculations allow us to distinguish between several possible assignments of the observed transitions, and hence determine the vibrational frequencies of the two previously unassigned A‐state stretching frequencies: ν3′=1180±2 cm−1 and ν1′=1011±2 cm−1. The ordering of these modes is different from that in the ground state (ν1″≳ν3″) and mechanisms for the ...
TL;DR: In this paper, an electronic transition in the isolated CaKr + ion with an origin at 14217 cm −1 has been observed in the resonant photodissociation spectrum, and the excited state in this transition arises from the Ca + 3 p 6 3 d [ 2 D ] + Kr [ 1 S ] atomic limit and is tentatively assigned as a 2 Σ + state.
TL;DR: In this article, the vibrational spectra of H2 in the collision with a proton at 30 eV in the laboratory frame are compared to results from calculations using the electron nuclear dynamics.
TL;DR: It is shown that for a metal with a broad conduction band, the asymmetry of the line shape of dipole-forbidden adsorbate vibrational modes is determined essentially by nonlocal optics effects, with negligible contribution from nonadiabaticity.
Abstract: A fully quantum-mechanical theory of infrared-reflection spectroscopy from adsorbate-covered metal surfaces is presented. In contrast to our earlier semiclassical theory [B. N. J. Persson and A. I. Volokitin, Surf. Sci. 310, 314 (1994)], which is valid only for parallel vibrational modes of atomic adsorbates, the present theory is applicable for arbitrary dipole-forbidden modes. It is shown that for a metal with a broad conduction band, the asymmetry of the line shape of dipole-forbidden adsorbate vibrational modes is determined essentially by nonlocal optics effects, with negligible contribution from nonadiabaticity. The theory is in good agreement with experimental data.
TL;DR: In this paper, the vibrational properties of a finite one-dimensional string-mass chain are studied experimentally and theoretically, and the theoretical predictions are made based upon the numerical solution to the wave equation.
Abstract: The vibrational properties of a finite one‐dimensional string‐mass chain are studied experimentally and theoretically. In the experiment both normal mode analysis and pulse analysis are used to obtain the eigenfrequencies of the string‐mass chain. The theoretical predictions are made based upon the numerical solution to the wave equation. The phononic band structure for a periodically massed string as well as Anderson localized gap modes for a disordered system are found. The theoretical and experimental results match satisfactorily well.
TL;DR: In this article, the rotational properties of the C-type bands ν14(1204 cm-1) and ν15(974 cm −1) of CF3CH2F have been analyzed at high and low resolution.
Abstract: The mid-IR spectrum of HFC-134a, CF3CH2F, entrained in a supersonic jet expansion has been measured at high and low resolution and the rotational structure of the C-type bands ν14(1204 cm–1) and ν15(974 cm–1) has been analysed along with the hot band ν15+ν18â†�ν18. Rotational constants have been obtained and used to simulate the band structure, enabling the rotational temperature in the jet to be estimated at 65 K. In addition, low-resolution far-IR spectra of CF3CH2F in a room-temperature gas cell have been recorded and the vibrational fundamentals more completely assigned. These results are compared with previous experimental values and those predicted from molecular orbital calculations.
TL;DR: In this article, the vibrational bands were assigned to the porphyrin skeletal and substituent modes on the basis of the mode description scheme developed for nickel octaethylporphyrin (NiOEP) with the aid of a normal-mode analysis of NiEPI, explicitly including the peripheral substituents.
Abstract: Nearly complete vibrational assignments have been obtained for a heme model, nickel etioporphyrin-I (NiEPI), using variable-wavelength resonance Raman (RR), and FT-Raman (FT-R), as well as infrared (IR) spectroscopy, on a series of isotopomers labeled at positions in the skeleton (15N, β-13C, meso-d4, 15N-meso-d4) and in the peripheral substituents (methyl-d12, ethyl-d8, and ethyl-d12). The vibrational bands are assigned to the porphyrin skeletal and substituent modes on the basis of the mode description scheme developed for nickel octaethylporphyrin (NiOEP) with the aid of a normal-mode analysis of NiEPI, explicitly including the peripheral substituents, i.e., the methyl and ethyl groups. The previously reported NiOEP force field was refined to account for the observed isotope shifts of NiEPI isotopomers. An important result is the requirement of relatively large, long-range force constants for methine bridge bonds on opposite sides of the porphyrin ring. These 1–8 and 1–9 interaction force constants are required to reproduce the frequencies and isotope shifts of six Cα-Cm stretching modes and especially to predict the relative order of the two highest-frequency Eu modes, v(Cα-Cm) (v38, ∼ 1570 cm−1) and v(Cβ-Cβ) (v37, ∼ 1600 cm−1). Most of the substituent (methyl and ethyl) vibrations are located in the RR and IR spectra. Strong RR enhancement of some substituent modes can be attributed to hyperconjugative interaction of the aliphatic groups with the porphyrin a1u orbital, as well as vibrational mixing of substituent modes with the nearby skeletal modes. © 1995 John Wiley & Sons, Inc.
TL;DR: In this paper, the vibrational heating of a surface bond by a hot electron gas is investigated with a quantum-mechanical model and its classical limit, and it is shown that the quantum model is important to correctly describe the multi-vibrational excitation at low temperature T v, where k B T v ≤ ǫ ≤ ϵ, the vibration energy quantum.
TL;DR: In this paper, the authors used model calculations to study how electron-transfer rates in solution depend on populations of specific vibrational levels and found a major increase in the electron transfer rate at small and large energy gaps when one or more quanta are in vibrations having large geometry changes during electron transfer.
Abstract: We use model calculations to study how electron-transfer rates in solution depend on populations of specific vibrational levels. The models are for nonadiabatic electron transfer with specific quantum populations in either a 2000 cm[sup [minus]1] or a 430-cm[sup [minus]1] vibrational mode, characteristic of inorganic complexes in which we have previously demonstrated quantum effects. We find a major increase in the electron-transfer rate at small and large energy gaps when one or more quanta are in vibrations having large geometry changes during the electron transfer, and the effects are greater for high-frequency modes. The rates for different energy gaps, the ratio of rates for different quantum numbers, and the populations of vibrational energy after the electron transfer were shown to be useful for testing specific molecular models of electron transfer. We also modified standard nonadiabatic models to provide rate predictions when excess energy is communicating among a subset of vibrational modes by intramolecular vibrational redistribution. This modification converts excess energy to an effective vibrational temperature, which is used in temperature-dependent Franck-Condon factors. 39 refs., 13 figs., 1 tab.
TL;DR: The vibrational spectrum of the Raman, infrared, and neutron inelastic-scattering measurements was calculated using first-principles density-functional theory as discussed by the authors, based on a combination of the all-electron local-density-functional method and group-theoretical analysis.
Abstract: The vibrational spectrum of the ${\mathrm{C}}_{70}$ molecule is calculated using first-principles density-functional theory Our approach is based on a combination of the all-electron local-density-functional method and group-theoretical analysis The calculated vibrational frequencies of the ${\mathrm{C}}_{70}$ molecule are found to be in good agreement with the experimental data available from Raman, infrared, and neutron inelastic-scattering measurements, and provide useful assignment for dormant modes
01 Mar 1995
TL;DR: In this paper, the anharmonic constants of trichlorosilane and -methane have been determined, with special emphasis to the values of x 1i, i = 1 to 6.
Abstract: Most of the anharmonic constants of trichlorosilane and -methane have been determined, with special emphasis to the values of x 1i , i = 1 to 6. In both molecules, there is a strong Fermi resonance between hydrogen stretch and bend vibrations and Coriolis interaction between v 2 and v 5 . Some irregularities in the hot band structures point to an interaction of v 1 with v 2 +2v 4 and other higher order interactions. In SiHCl 3 , x 13 and x 16 are near 0, in agreement with a rule that nondiagonal anharmonicities between high- and low-frequency vibrations tend to be small. In CHCl 3 , the corresponding values are larger, though still small. We discuss a possible correlation of such values with the frequency change of one of the vibrations, if the bond corresponding to the other one is dissociated. Ni(CO) 4 is quoted as a further example. The data set could help in calculations of vibrational relaxation rates
TL;DR: In this paper, the authors discuss the origin of the 3.3 μm emission band and its major satellite band at 3.40 μm and show that the position and width of this band are consistent with the carriers being free PAH molecules.
TL;DR: In this article, the potential energy distribution for the nonplanar modes from a refinement calculation is discussed, and the ideal-gas thermodynamic functions are evaluated using the vapor phase vibrational wavenumbers and the previously reported moments-of-inertia.
TL;DR: In this paper, the first moment of the 6A1g to 4T1g excitation band and the associated emission band of Mn2+-doped ABF3 perovskites are investigated in the 9-300 K temperature range.
Abstract: The thermal shifts undergone by the first moment of the 6A1g(S) to 4T1g(G) excitation band and the associated emission band of Mn2+-doped ABF3 perovskites are investigated in the 9-300 K temperature range. It is found that these shifts are similar for the whole series and have average values of +150 and +450 cm-1 for excitation and emission, respectively. Both the sign and the magnitude of these different thermal shifts are explained in terms of (i) the phonon assistance mechanism required to gain intensity of the parity-forbidden transitions, (ii) the quadratic electron-phonon coupling and (iii) thermal expansion effects. To achieve this analysis a previous discussion upon the nature of the vibrational modes seen in the optical spectra is carried out. It is stressed that the impurity vibrational mode displaying h(cross) omega g=570 cm-1 in the emission spectrum of KMgF3:Mn2+ exhibits a value of 540 cm-1 in the corresponding excitation spectrum. This situation, which is also found for other modes seen in the optical spectra of KMgF3:Mn2+, indicates that the mode (though associated with the LO3 branch of KMgF3) is not a pure mode of the lattice but displays a kind of resonant character. As a salient feature the calculated thermal shifts are based on the experimental shifts experienced by the frequencies of the optical and acoustic modes on going from the ground 6A1g to the excited 4T1g state of MnF64-. At variance with findings for the R lines in Cr3+ and V2+, it is clearly demonstrated that the explicit and implicit contributions to the thermal shift of the zero-phonon line in MnF64- are similar and both induce red shifts upon heating. Moreover the present analysis reveals that the explicit contribution to the thermal shift undergone by the zero-phonon line of KMgF3:Mn2+ is mainly dominated by the odd-parity low-energy modes. The calculated thermal shifts reproduce reasonably well the experimental data.
TL;DR: In this paper, an extension of the multiconfigurational SCF approach for the resolution of the vibrational problem is presented; it follows the philosophy of the CASSCF method developed in Quantum Chemistry and allows a more complete treatment of anharmonic mode couplings, converges much faster and gives a clearer physical insight of vibrational interactions.
Abstract: An extension of the multiconfigurational SCF approach for the resolution of the vibrational problem is presented; it follows the philosophy of the CASSCF method developed in Quantum Chemistry. The new method allows a more complete treatment of anharmonic mode couplings, converges much faster and gives a clearer physical insight of vibrational interactions. This is exemplified by the calculation of infrared transition moments in the H2O and D2O isotopomers of the water molecule. It is shown how this property varies with the quality of the wave function when vibrational resonances occur. A detailed analysis by means of this new VCASSCF method demonstrates the crucial importance of excited bending oscillators in the intensity of some pure stretching transitions.
TL;DR: In this article, the authors obtained vibrational spectra of molecular materials at simultaneous high pressure and high temperature using the combined techniques of shock wave compression and coherent Raman spectroscopy.
TL;DR: In this article, the authors measured the far-infrared spectrum of gaseous CH 3 SiH 3 with a Fourier transform spectrometer between 180 and 380 cm −1 under relatively large pressure-path length conditions.
TL;DR: In this paper, the laser-induced fluorescence spectra of jet-cooled o -, m - and p -chlorotioluene molecules in the S 1 state were reported.
Abstract: The laser-induced fluorescence spectra of jet-cooled o -, m - and p -chlorotioluene molecules in the S 1 state are reported. The fluorescence excitation spectra of these molecules exhibit a variety of vibrational modes in the S 1 state. The spectra of m - and p -chlorotoluene show low-frequency bands up to 200 cm −1 above the S 1 origin, which are assigned to internal rotational modes of the methyl group. From 300 cm −1 up to approximately 1500 cm −1 , sharp vibrational bands appear; these are assigned by measuring the dispersed fluorescence spectra on excitation of each vibrational band. The vibrational energies of the CCl symmetric stretching mode for o -, m - and p -chlorotoluene molecules are 341 cm −1 , 378 cm −1 and 360 cm −1 in the S 1 state respectively. Other prominent normal modes are also assigned.