A theoretical study on the ionization of OCS with an analysis of vibrational structures of the photoelectron spectrum

 Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying ionic states (1, 2²Π, and 1, 2²Σ⁺) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectrum. Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001     

Probing the vibrational spectroscopy of the deprotonated thymine radical by photodetachment and state-selective autodetachment photoelectron spectroscopy via dipole-bound states

Deprotonated thymine can exist in two different forms, depending on which of its two N sites is deprotonated: N1[T–H]^– or N3[T–H]^–. Here we report a photodetachment study of the N1[T–H]^– isomer cooled in a cryogenic ion trap and the observation of an excited dipole-bound state. Eighteen vibrational levels of the dipole-bound state are observed, and its vibrational ground state is found to be 238 ± 5 cm^–1 below the detachment threshold of N1[T–H]^–. The electron affinity of the deprotonated thymine radical (N1[T–H]˙) is measured accurately to be 26 322 ± 5 cm^–1 (3.2635 ± 0.0006 eV). By tuning the detachment laser to the sixteen vibrational levels of the dipole-bound state that are above the detachment threshold, highly non-Franck–Condon resonant-enhanced photoelectron spectra are obtained due to state- and mode-selective vibrational autodetachment. Much richer vibrational information is obtained for the deprotonated thymine radical from the photodetachment and resonant-enhanced photoelectron spectroscopy. Eleven fundamental vibrational frequencies in the low-frequency regime are obtained for the N1[T–H]˙ radical, including the two lowest-frequency internal rotational modes of the methyl group at 70 ± 8 cm^–1 and 92 ± 5 cm^–1.     

Thermal energy charge transfer reactions of Ar+ ions with HBr and DBr molecules

HBr⁺ (A²Σ⁺-X²Π_i) and DBr⁺ (A²Σ⁺-X²Π_i) emissions are found up to v′=1 and v^′=2, respectively, from the thermal energy charge transfer reactions of Ar⁺ with HBr and DBr molecules in a flowing afterglow apparatus. Both A-state vibrational distributions have a peak at the lowest vibrational level, which are inconsistent with those expected from the energy resonance and/or Franck-Condon factors for ionization. This discrepancy is explained in terms of the distortion of target molecules by approach of reactant ions. Both A-state rotational distributions show that energies partitioned into rotation decrease with increasing vibrational levels, whereas the internal energy is nearly constant for all vibrational levels. The vibrational and rotational distributions obtained suggest that the reaction occurs at a relatively short distance and the product has a broad translational energy distribution.     

Dissociative excitation of water by metastable argon

The reaction Ar(²P_2,0) + H₂O → Ar + H + OH(A²Σ⁺)was studied in crossed molecular beams by observing the luminescence from OH(A²Σ⁺). No significant dependence of the spectrum on collision energy was found over the 22–52 meV region. Spectral simulation was used to obtain the OH(A) vibrational distribution and rotational temperature, assuming a Boltzmann rotational distribution. Since predissociation is known to strongly affect the rovibrational distribution, the individual rotational state lifetimes were included in the simulation program and were used to obtain the average vibrational state lifetimes. Excellent agreement with experiment was obtained for vibrational population ratios N₀/N₁/N₂ of 1.00/ 0.40/0.013 and a rotational temperature of 4000 K. Correction for the different average vibrational lifetimes gave formation rate ratios P₀/P₁/P₂ of 1.00/0.49/0.25. The differences between these results and those from flowing afterglow studies on the same system are discussed. Three reaction mechanisms are considered, and the vibrational prior distributions are calculated from a simple density-of-states model. Only fair agreement with experiment is obtained. The best agreement for the mechanisms giving OH(A) in two 2-body dissociation steps is obtained by assuming 1.0 eV of internal energy remains in the second step. The OH(A) vibrational population distribution of the present work is similar to that found in the photolysis of H₂O at 122 nm, where there is 1.10 eV of excess internal energy.     

Predictions of the bond length and vibrational frequency of Ge2

We present a pseudopotential local spin density calculation of the bond length, vibrational frequency, and binding energy for the ³Σ_g^? state of the germanium dimer. Predictions for the equilibrium bond length and vibrational frequency are given. An overestimate of the binding energy is obtained; this is consistent with other local spin density calculations for sp bonded diatomic molecules.     

Ab initio computation of vibrational relaxation rate coefficients for the collisions of CO2 with helium and neon atoms

Ab initio calculations of rate coefficients are reported for the vibrational relaxation of CO₂ molecules in collision with helium and neon atoms. Self consistent-field computations have been performed to parameterise simple three-dimensional potential energy functions which have been used in vibrational close-coupling, rotational infinite-order-sudden calculations of rate coefficients. Excellent agreement is obtained between the calculated and experimental rate coefficients for the deactivation of the (01₁0) vibrational level in the He + CO₂ system at temperatures of 300 K and above. The ab initio predictions of rate coefficients for relaxation of CO₂ vibrational levels such as (10⁰0) and (02⁰0) should be useful in computer simulations of CO₂ lasers.     

Normal coordinate analysis of porphin and its derivatives based on the solution of the inverse spectral problem for porphin and Cu porphin—III. Interpretation of vibrational spectra of metal complexes of octamethylporphin and octaethylporphin

The valence force field obtained for Cu porphin from the solution of the inverse spectral problem is used for calculating normal vibrations of Cu octamethylporphin and Cu octaethylporphin and their isotope-substituted derivatives (¹H-²H, ¹⁴N-¹⁵N). The interpretation of vibrational spectra of octamethylporphin and octaethylporphin metal complexes is given. Insufficient presentation of vibrational modes in terms of potential energy distribution to predict isotope shifts of vibrational frequencies is noted.     

A numerical study of time-dependent schr?dinger equation for multiphoton vibrational interaction of NO molecule, modelled as Morse oscillator, with intense far-infrared femtosecond lasers

For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schr?dinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities,I = 1 × 10⁸, 1 × 10¹³, 5 × 10¹⁶, and 5 × 10¹⁸ W cm⁻² respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed. Dedicated to Professor C N R Rao on his 70th birthday An erratum to this article is available at .     

Theoretical study on the vibrational structure of S0 thiophosgene from the origin to dissociation

In this work, using our vibrational variational calculation method and a recently derived refined quartic potential energy surface for S₀ thiophosgene, we have carried out large scale vibrational calculations to analyze the vibrational structure of this electronic state in the whole range of vibrational excitation energies down from the origin and up to the dissociation limit (at ↼20,000 cm^↙1). In the lower excited vibrational range we have achieved satisfactory coincidence of calculated to experimentally measured frequencies, while at the higher vibrational excitations our main objective has been to estimate what part of the available vibrational level density is effectively involved into the vibrational mixing and IVR. The results from our calculations have been compared to the available experimentally obtained dataset (obtained from synchrotron IR, SEP and LIF spectra) as well as to conclusions from the analyses by other authors using local coupling models.     

Ab initio rovibrational states and infrared spectrum of RbCN

Using an ab initio potential surface the rovibrational states of RbCN are calculated in the atom-(rigid) diatom formalism. From these, infrared transition intensities and vibrationally averaged dipole moments are obtained, using an ab initio dipole surface. The lower vibrational states can be labeled by bend and stretch, for which the fundamental frequencies are 100.4 and 258.0 cm⁻¹. At energies higher than 500 cm⁻¹, many overlapping resonances are found and the vibrational labeling breaks down. The calculated ground-state rotational constants are A = 2.269 cm⁻¹, B = 0.106 cm⁻¹ and C = 0.100 cm⁻¹, with an inertial defect ΔI = 0.687 amu Ų. For the higher vibrational states these parameters are used to study the increasing floppyness of the molecule and its behaviour as an effective linear isocyanide in excited states. At low temperature, the vibrational absorption spectrum only contains the fundamental transitions plus a transition caused by a Fermi resonance between the stretch fundamental and the third bending overtone. At high temperature, the chaotic and quasi-linear states have a marked effect on the absorption spectrum.     

Gegenbauer polynomials in a theoretical study of the vibrational structure of the Ca+–H2 system

This work presents an application of Gegenbauer polynomials in vibrational calculations. We illustrated that by example calculations of vibrational structure of the Ca⁺–H₂ exciplex, in the state correlated with 3D calcium ion state. For this case Gegenbauer polynomials are used for formation of a basis set for a bending mode. We showed that this basis set leads to a faster convergence of results than a basis set formed from Legendre polynomials. Additionally we compared vibrational structure obtained in this manner with results of discrete variable representation-distributed Gaussian basis (DVR–DGB) method.     

Observation of the fourth positive system of CO in dissociative recombination of vibrationally excited CO+2

The CO fourth positive system obtained by dissociative recombination of CO₂⁺(X̃²π_g) ions has been observed under various conditions of CO₂⁺ vibrational excitation. It is shown that the CO(A¹π) vibrational distribution is directly linked to CO⁺₂ excitation. Implications for planetary airglows are discussed.     

BaO(X 1Σ+) vibrational relaxation

Vibrationally excited BaO(X ¹Σ⁺) was produced by reacting Ba atoms with O₂ under “jet flow” conditions in which the convective flow velocity was large compared with the diffusion velocities so that the relaxation could be spatially resolved. The vibrational level populations were determined by laser-induced fluorescence measurements. By using modeling calculations to fit the spatial variation of the apparent vibrational temperature, we obtained a vibrational relaxation rate for BaO(X ¹Σ⁺), ν = 1 → ν = 0, by Ar, of 9 × 10^?13 cm³/molecule s.     

荧光色散谱对FeS(X5△)振动常数的实验确认

Based on previous laser-induced fluorescence excitation spectroscopy work, the vibrational constants of neutral FeS in the X⁵△ electronic state were obtained by directly mapping the ground-state vibrational levels up to v″=3 using conventional laser-induced dispersed fluorescence spectroscopy. The vibrational frequency of FeS(X⁵△) (518±5 cm-1) agrees well with that reported in a recent PES measurement (520±30 cm-1) [J. Phys. Chem. A 107, 2821 (2003)] which is the only one prior experimental vibrational frequency value for the ⁵△ state of FeS. Careful comparisons of our experimental results and those documented in the literature (mainly from theoretical predictions) suggest that the ground state of FeS is ⁵△ state.     

Experimental and Theoretical Vibrational Study of the Oxotetrachlorochromate(V) Anion in [AsPh4][CrOCl4]

Infrared and Raman spectra were obtained for tetraphenylarsonium oxotetrachlorochromate(V), [AsPh₄][CrOCl₄]. Equilibrium geometry and vibrational frequencies for the anion, CrOCl₄^?, were studied employing Density Functional Theory (DFT) methods. A comparative theoretical study was performed in order to determine the best level of theory and basis set to reproduce the experimental structure parameters and vibrational frequencies. Such frequencies served as a basis for the calculation of the scaled quantum mechanical (SQM) force field for the anion. The obtained results were compared with those obtained previously for the VOCl₄^? anion.     

A DFT analysis of the vibrational spectra of nitrobenzene

Raman and FTIR, spectra of nitrobenzene, nb, and its isotopomers, nb-¹⁵N, nb-¹³C₆ and nb-d₅, were obtained and the fundamental vibrational modes assigned with the aid of a B3LYP/6-311+G** calculation, without the need for scaling of the force constants. The changes in vibrational coupling between the nitro and benzene groups upon certain isotopic substitutions are well modelled by the calculation, which is able to reproduce the isotopic shifts in frequencies for the nitro vibrations, as well as changes in IR intensities.     

A joint vibro-electronic mechanism in the dissociation of molecular hydrogen in nonequilibrium plasmas

A new mechanism Of H₂ dissociation in electrical discharges (10¹¹ ? n_e ? 10¹² cm^?3, 2.10^?16 ? E/N ? 3.10^?16 V cm², 300 ? T_g ? 1000 K, 3 ? p ? 30 torr) is presented and discussed. In this mechanism, called joint vibro-electronic mechanism (JVE), the electrons of the discharge create a strong vibrational disequilibrium with respect to the gas temperature (T_g) and promote electronic transitions from all vibrational levels of ¹Σ_g H₂ state to the repulsive ³Σ_u one. Moreover the V-V (vibration-vibration) and V-T (vibration-translation) energy exchanges are considered for building up the vibrational distribution of ¹Σ_g state. A complete set of e - D cross sections (e + H₂(¹Σ_g,ν) → e + H₂ (³Σ_u) → + 2H, ν = 0,14) is calculated by using an extension of the semiclassical Gryzinski theory in combination with the Franck-Condon principle. Dissociation rates calculated according to JVE are larger either than those obtained by the pure vibrational mechanism (PVM) discussed in our previous work or than those from the direct electronic impact mechanism (DEM) from the ground vibrational level. The behaviour of JVE rates as a function of gas temperature (T_g), of E/N, of electron density (n_e) and of pressure is then reported. The results show strong differences as compared, with the corresponding values obtained, with PVM. Finally the influence of the atoms as well as their recombination on the dissociation rates is discussed. The results have been obtained by solving a system of vibrational master equations.     

Molecular mechanics investigation of some acrylic polymers using SPASIBA force field

The First generation SPASIBA force field is used to study normal vibrational modes of PMMA, and then extended to other thermoplastic polymers, namely PMA, PMAA and PAA, in order to determine its parameters transferability. To this end, FTIR and FTR spectra of pure PMMA samples, prepared by the emulsion polymerization of MMA and initiated by sodium, are recorded in 400–3500 cm⁻¹ and 200–3500 cm⁻¹, respectively. A detailed vibrational analysis was performed on the obtained spectra and the observed frequencies are assigned to their respective vibrational modes, supported by potential energy distribution (PED) analysis. Our numerical results reveal an RMS value of 7.8 cm⁻¹ corresponding to IR wavenumbers and 8.7 cm⁻¹ relatively to Raman wavenumbers. Our vibrational calculations on PMA, PMAA and PAA polymers reveal that the parameters transferability criterion, established by Shimanouchi, is verified for the SPASIBA force field.     

Time dependent wave packet treatment of 2ΠgN2− and 3Σ−NO− shape resonances using two‐dimensional surfaces for electron‐N2 and NO interactions

The ²Π_gN and ³Σ^?NO^? resonances in electron‐N₂ and NO collisions have been treated using both nuclear and electronic degrees of freedom and a two‐dimensional (2D) time dependent wave packet approach to ascertain the importance of nonlocality in electron–nuclear interaction. The results so obtained are compared with vibrational excitation cross‐sections obtained experimentally and those from other theoretical/numerical approaches using 1D local complex potential, 2D model with a combination of the exterior complex scaling method and a finite‐element implementation of the discrete‐variable representation. The results obtained provide detailed insight into the nuclear dynamics induced by electron–molecule collision and reveal that while for resonant excitation of lower vibrational modes, the nonlocal effect may not be as critical but importance of nonlocal effects may increase with increase in quanta of resonant vibrational excitation. © 2012 Wiley Periodicals, Inc.     

Third-order RKR procedure

Potential energy curves for the X¹Σ⁺state of ⁶LiH, ⁷LiH and ⁶LiD, ⁷LiD molecules have been calculated by the third-order RKR inversion procedure by including the Kaise correction. The results are in agreement with previously obtained curves by other authors using differents methods. As a check, the exact vibrational eigenfunctions, appropriate to these potentials, are obtained by direct numerical solutions of the radical Schrödinger equation.