Intramolecular vibrational modes of polychlorodibenzo-p-dioxines of the D 2h symmetry

The infrared and Raman spectra of the octachlorodibenzo-p-dioxine molecule are measured and all normal vibrational modes of the molecule are calculated. Each vibrational mode was assigned to the vibrations of certain functional groups of atoms in the molecule, taking into account the local symmetry characteristics of the vibration mode. A correlation of vibrational modes by their shape was established in a series of molecules: dibenzo-p-dioxine, 2,3,7,8-tetrachlorodibenzo-p-dioxine, and OCDX. The influence of substituents on vibrational frequencies was also examined.     

Vibrational structure in the valence electron spectra of pyridine and pyridine—d5

The He(I) electron spectra of pyridine and pyridine-d₅ have been recorded. Distinct vibrational progressions are observed in the first and fourth electronic bands and a vibrational analysis is made. The isotopic effect on the vibrational energies is found to be helpful in the assignment of the vibrational peaks.By consideration of highly resolved spectra the vibrational interpretation of certain bands in the photoelectron spectra of pyridine and pyridine-d₅ has been accomplished. The spectra of the two species display differences due to isotope exchange but are nevertheless similar in structure. This is of great help in the vibrational assignment.     

Density of vibrational states in amorphous solid media: Measurement by single-molecule spectroscopy

The energy spectrum of low-frequency vibrational modes in amorphous polyisobutylene doped with chromophore tetra-tert-butylterrylene molecules has been measured. The technique for measuring the spectra of vibrational modes in solid amorphous media by single-molecule spectroscopy is described. The measured spectrum is compared with the data on the density of vibrational states (bosonic peak) in pure polyisobutylene, which were obtained by inelastic neutron scattering. It is shown that incorporation of small amounts of tetra-tert-butylterrylene into polyisobutylene did not significantly change the low-temperature vibrational dynamics of the matrix.     

Vibrational excitation of a molecule by a resonance current

Correct expressions are obtained for calculating a tunnel-resonance current through molecules. The participation of molecular vibrations in the resonance charge transfer through a molecule and vibrational excitation of the molecule are determined by the reorganization energy E _r of the vibrational system depending on the displacement of the equilibrium position of vibrational modes in passing from the neutral molecule to the resonance state of a molecular ion. The mean excitation energy of the molecule during the propagation of an elementary charge changes from E _r at the voltage across electrodes close to the threshold up to 2E _r at voltages considerably exceeding the threshold voltage. An expression is obtained for the stationary vibrational temperature of the molecule, which is proportional to the resonance current.     

Heterogeneous relaxation of molecule vibrational energy on metals

A mechanism of heterogeneous relaxation of a molecule vibrational energy on metal via conduction electrons is proposed. The probability of vibrational transition W of a molecule adsorbed on metal surface is calculated. The not very sharp dependence of W on the distance between the molecule and the metal surface, on metal parameters and on the molecular vibrational quantum provides a satisfactory explanation of the experimental data available.     

Intermolecular vibrational relaxation upon multiphoton excitation of triplet molecules by a CO2 laser

Intermolecular vibrational relaxation is studied in mixtures of polyatomic molecules (benzophenone and fluorene) with bath gases after multiphoton excitation of the triplet molecules by CO₂ laser radiation. The dependences of the decay rate and the intensity of laser-induced delayed fluorescence on the laser energy density E _CO2 and pressure P _fg of bath gases are analyzed. They are found to be different for the fast and slow components of delayed fluorescence, which decays nonexponentially. It is shown that a change in the decay rate of the fast fluorescence component with increasing pressure P _fg is governed by the properties of vibration-translation relaxation. The efficiency β of this process is estimated in a broad range of vibrational energies. It is found that β weakly changes with increasing E _vib upon excitation of molecules to high vibrational levels. The features of intermolecular vibrational relaxation at high densities of anharmonically coupled vibrational states are discussed.     

Towards an explanation of collisionless multiple-photon laser dissociation of SF6

The rapidity and high degree of molecular vibrational excitation by the absorption of ir laser light in SF₆ and other molecules may be due in large part to the anharmonic splitting of excited vibrational states. Anharmonic splitting of an overtone or combination vibrational level (i) is possible only in molecules with degenerate vibrational states, (ii) can be comparable in magnitude to the net anharmonic shift of the level, (iii) is generally much larger than the rotational shifts which have previously been proposed as an explanation for the dissociation of SF₆. We find that consecutive nearly resonant transitions are possible in SF₆ up to υ₃ = 5 to 10.     

Millimeter wave rotational spectrum of deuterofulminic acid,DCNO, in excited vibrational states

Rotational transitions of DCNO in the vibrational states 00002, 00003, 00020, and 00011 have been measured and analyzed. These results complete the presentation of assigned millimeter wave transitions of DCNO.The analysis of rotational l-type resonance in the 00002 and 00020 states is more satisfactory in the case of DCNO than in that of HCNO due to the absence of accidental resonances. The values obtained for the vibrational anharmonicity constant g₅₅ for 00002 and 00003 agree within experimental error with those found from the vibrational spectrum.An ambiguity in the assignment of the symmetry of the transitions in the four components of the 00011 vibrational state is discussed.     

HCNO as a semirigid bender: The degenerate ν4 state

The semirigid bender Hamiltonian for fulminic acid HCNO (Bunker, Landsberg, and Winnewisser, J. Mol. Spectrosc.74, 9–25 (1979)) is extended. The extended Hamiltonian describes the manifold of large amplitude vibrational states (due to the ν₅ HCN bending mode) superimposed on a high frequency vibrational state involving excited quanta of the ν₄ CNO bending mode. Such high frequency vibrational states may be degenerate when the large amplitude coordinate is zero, and the semirigid bender Hamiltonian is modified to account for the ν₄ vibrational angular momentum around the molecular axis in the linear limit, and for l-doubling effects. The extended Hamiltonian is used to fit HCN bending and rotation energy level separations for HCNO superimposed in the ν₄ fundamental level. It is found that the effective HCN bending potential in the ν₄ state is very similar to that in the high frequency vibrational ground state. The results obtained confirm the conclusion reached by Bunker, Landsberg, and Winnewisser: HCNO is linear at equilibrium.     

Emission spectrum of MgCl molecule in 5030-4380Å

The emission spectrum of diatomic magnesium chloride molecule has been reinvestigated in the region 5030-4380 Å (B ²Σ⁺ —A ²Π transition) at a higher dispersion. The vibrational assignments of the bands are confirmed by observing the vibrational isotope shifts due to isotopes of magnesium and chlorine. Precise values of the vibrational constants are determined for theB ²Σ⁺ state.     

High resolution angle-resolved photoelectron spectrum of CO2, excited with polarized resonance radiation

The He(I) excited and angle-resolved photoelectron spectrum of CO₂ is investigated using a focussing VUV-polarizer. High resolution combined with the additional information given by comparing spectra taken at different angles permits detailed analysis of the vibrational structure. β-values are given for all vibrational components hitherto observed in the photoelectron spectrum of the ≈X, ≈A,≈B and ≈C electronic bands. Single excitations of the v₃ mode with vibrational energies 181 meV in the estate and 279 meV in the ≈B-state are reported. The peak at 360 meV vibrational energy in the (≈C-state is reinterpreted as a single v₃ excitation. The β-values of the most intense peaks are also measured using Ne(I) (16.67 and 16.85 eV), Ne(II) (26.86 and 26.95 eV) and He(II) (40.81) resonance radiations.     

Characterisation of electric discharge in hollow electrode Z-pinch device by means of Rogowski coils

In this paper, the energy spectra of the general molecular potential are obtained using the asymptotic iteration method within the framework of non-relativistic quantum mechanics.With the energy spectrum obtained, the vibrational partition function is calculated in a closed form and is used to obtain an expression for other thermodynamic functions such as vibrational mean energy U, vibrational mean free energy F, vibrational entropy S and vibrational specific heat capacity C. These thermodynamic functions are studied for the electronic state \(\mathrm{X}^{1}\Sigma _g^+ \) of \(K_2\) diatomic molecules.     

Normal mode analysis of alkenes by the consistent force field

A consistent force field for the simultaneous analysis of vibrational frequencies, conformations and thermodynamic properties of alkenes is applied to the normal mode analysis of cis- and trans-2-butene, 1,2-dimethyl-cyclopentene, cyclohexene, trans,trans,trans-1,5,9-cyclododecatriene, 1,4-cyclohexadiene, and cyclopentene. Special attention is given to the torsional modes of the 2-butenes and to the bending modes of the HCCH group. A number of reassignments are suggested. The simultaneous vibrational analysis of strained and unstrained molecules is achieved by considering nonbonded interactions and their influence on equilibrium conformations and vibrational modes.     

Microwave spectroscopy of OCS in highly excited vibrational states through energy transfer from N2

The efficient vibrational energy transfer between the first excited vibrational state of N₂ and the asymmetric stretching vibrational state of OCS has allowed the observation of many pure rotational lines in different vibrational states of OCS up to 4101 cm^?1: (00⁰1), (01¹1), (02^l1), (10⁰1), (00⁰2), (21¹0), (03^l0), (04^l0), and (05^l0). Accurate values of some rotational, centrifugal distortion and l-doubling constants are determined.     

Surface vibrational excitations of O in the p(2 × 2)O and c(2 × 2)O structures on Ni(100)

Surface vibrational excitations of O chemisorbed on the clean Ni(100) surface have been investigated by high-resolution electron energy loss spectroscopy (EELS). The observed vibrational losses in the Ni(100) p(2 × 2)O and Ni(100) c(2 × 2)O surface structures are 53.0 ± 0.5 and 39.5 ± 0.5 meV respectively. The unexpectedly large change in the vibrational excitation energy is attributed to a low potential barrier for oxygen dissolution into the Ni substrate.     

Influence of short-and long-range interaction forces on the efficiency of collisional vibrational energy transfer in the vibrational quasi-continuum

Based on measurements of the time-resolved delayed fluorescence, the influence of universal interactions on the collisional vibrational energy transfer is studied in mixtures of vibrationally excited polyatomic molecules (acetophenone, benzophenone, and anthraquinone) with inert bath gases (Ar, C₂H₄, SF₆, CCl₄, and C₅H₁₂). From the dependences of the decay rates of delayed fluorescence on bath gas pressure, the efficiencies of the establishment of vibrational (V-V relaxation) and thermal (V-T relaxation) equilibrium after excitation of molecules into the vibrational quasi-continuum of a triplet state are estimated. The main emphasis is on studying the dependences of the efficiency of collisional vibrational energy transfer on temperature and the molecular characteristics of collision partners. It is found that the efficiency increases with the complication of the structure of bath gases for the V-V process and decreases upon the increasing of their mass for the V-T process. For the temperature range 273–553 K, the negative temperature dependence of the V-V transfer probability and the positive (Landau-Teller) dependence of the V-T transfer probability were obtained. It is concluded that the above regularities reflect the dominant role of long-range attractive forces in initiating the quasi-resonant V-V transfer and of short-range repulsive forces in the V-T transfer of vibrational energy.     

Gamma deexcitation of the 180m Ta isomer

Vibrational states built on the K ^π = 9^? isomer and on the ground state (K ^π = 1⁺) in ¹⁸⁰Ta are calculated within the quasiparticle-phonon nuclear model using the ¹⁷⁸Hf nucleus as a core. A procedure for calculating the rates of K-allowed γ-ray transitions from vibrational states built on the isomer to those built on the ground state is presented. The probabilities of two-step processes consisting of a dipole excitation of the isomer and successive E1 and E2 transitions from them to vibrational states built on the ground state of the ¹⁸⁰Ta nucleus are calculated. Two-step transitions from the isomer to vibrational states below 2.7 MeV and to the vibrational states built on the ground state appear to be very weak. There are many E1 transitions from the vibrational states built on the isomer to the vibrational states built on the ground state. They are weak and cannot be responsible for the strong deexcitation of ^180m Ta in the relevant (γ, γ′) reaction. A decisive role is played by collective E2 transitions from dipole excitations in several excitation energy intervals ranging between 2.7 and 4.0 MeV. These highly intense K-allowed two-step γ-ray transitions can be responsible for the strong deexcitation of the ^180m Ta state in the (γ, γ′) reactions.     

Coupling of vibration,rotation, and electron spin in multiplet states

The effective Hamiltonian of Van Vleck (1) for energy calculations of rotating molecules in multiplet states, is extended to include the effect of vibrational angular momentum, within a given nondegenerate electronic state. H_C and H_S operators are defined, to account for vibration-rotation (Coriolis) and spin-vibration interactions, respectively. Such interactions are discussed for degenerate E vibrational states of symmetric tops, as well as for the occurrence of vibrational angular momentum involving different vibrational states, with accidentally low energy separation. Following the classification of Hund's case (b) for the spin-rotation wave function (coupled representation), we find that H_C operators do not mix different F components, whereas H_S operators give also matrix elements between F components differing by one unit in the quantum number N, for given J.     

The 260 nm absorption spectrum of benzene: Selection rules and band contours of vibrational angular momentum components

The role of vibrational degeneracies and vibrational angular momentum in the 260 nm absorption spectrum of benzene is further examined. Degenerate Herzberg-Teller terms are set down through third order with specific identification of vibrational symmetries capable of inducing intensities (Table II). These terms provide a basis for predicting the Δv selection rules, the signed vibrational angular momentum selection rules, and the vibrational angular momentum component energy splittings for all vibronic transitions. A new parameter, χ, is developed which can be used to predict the rotational band contour of any vibronic component transition. These developments underlie the systematic reexamination of assignments which is given in Paper III of this series.     

A comprehensive model to predict the microwave spectrum of propyne in the region 17–70 GHz for the ground and v10 = 1, 2, 3, 4, 5 vibrational states

A comprehensive model for predicting rotational frequency components in various v₁₀ vibrational levels of propyne was developed. A number of components of the rotational spectra in the ground and v₁₀ = 1, 2, 3, 4 excited vibrational states of propyne in the frequency range 17–70 GHz have been obtained. Molecular constants for these vibrationally excited states have been determined from more than 100 observed rotational transitions. From these experimentally observed components and a model based upon first principals for C_3v molecules, rotational constants have been expressed in a form which enables one to predict rotational components for vibrational levels for propyne up to v₁₀ = 5. The model also appears to be useful in predicting rotational components in more highly excited vibrational levels but data were not available for comparison with the theory. Experimentally measured frequencies are presented and compared with those calculated using the results of basic perturbation theory.