摘要:

Portions of the lowest singlet and triplet potential energy surfaces of CO2S were investigated byab initioself-consistent field methods with the inclusion of electron correlation by Møller-Plesset perturbation theory. Earlier experiments indicated that the reaction of oxygen atoms with carbonyl sulphide occurred by a direct stripping mechanism to form the products CO(1Σ+) and SO(3Σ-). This reaction may proceed on the singlet potential energy surface through an OCSO intermediate. This singlet surface lies approximately 60 kcal mol-1below the triplet and the barrier heights leading to the OCSO singlet minima are less than 30 kcal mol-1. Multiple intersystem crossings are required to connect ground state reactants to products as both have triplet multiplicity in contrast to the singlet intermediates. Two sets of bentcisandtranstriplet structures were located, the SCOO and OCOS isomers, both of which are considerably higher in energy than the singlet species. Another series of low-lying singlet structures was found and these include the lowest energy intermediate on either surface, an asymmetric ring isomer with sulphur, oxygen and carbon forming a three-membered ring and a carbonyl group.

ISSN:0026-8976    

DOI:10.1080/00268979300101541

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

From the analysis of its rotational spectrum, phthalan appears to be non-planar with a barrier of about 40 cm-1hindering the ring puckering of the five membered component. This result is in contrast to both a far infrared investigation (Smithson, T. L., Duckett, J. A., and Wieser, H., 1984,J. phys. Chem.,88,1102) that suggested the molecule to be planar, and a single vibronic level fluorescence spectrum (Hassan, K. H., and Hollas, J. M., 1991,J. molec. Spectrosc.,147,100) that suggested a barrier hindering a twisting motion.

ISSN:0026-8976    

DOI:10.1080/00268979300101551

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A separable one-dimensional model of anisotropic hard molecules recently introduced in the literature is worked out to compute the radial density profiles and the angular distributions in the vicinity of a hard wall. Its results are tested against Monte Carlo simulations performed on a system of aligned hard ellipses confined in a segment. We find that the model provides a good description of such a system whenever the angular mobility of the particles is small enough. Accordingly, we find that the density profiles are better described for high pressures, and the angular distributions when they are close to the wall. Nevertheless, the distribution functions in the bulk have the same functional shape but for a smaller eccentricity. Such effective eccentricities follow a power law extremely well when compared with the true ones.

ISSN:0026-8976    

DOI:10.1080/00268979300101561

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A time resolved experiment on the lowest lying states of barium fluoride has been performed by applying laser resonance methods in the near infrared and green-blue wavelength regions. The A2Π and B2Σ+states have been examined using Ti:sapphire laser excitations in the 710–850 nm wavelength region. The C2Π state was examined using the 496·5 nm Ar+laser line and the lifetime of this state was in accordance with earlier measurements. The lifetimes obtained for the BaF molecule were: A2Π3/2, 46·1 ± 0·9 ns; B2Σ+, 41·7 ± 0·3 ns.

ISSN:0026-8976    

DOI:10.1080/00268979300101571

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Based on the symmetric method, analytical expression or recursive relations for the spectral moments of the C20,C24, C26, C28, C30, C32, C36, C38, C40, C42, C44, C50and C60fullerene cage clusters are obtained by factoring the original graphs and the corresponding characteristic polynomials into their smaller subgraphs and subpolynomials. We also give numerical results for the spectral moments. It is demonstrated that the symmetric method is feasible in enumerating the moments as well as factoring the characteristic polynomials for fullerene cages.

ISSN:0026-8976    

DOI:10.1080/00268979300101581

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

About 1100 lines of the 2v4∓2perpendicular component and about 600 lines of the 2v40parallel component of the 2v4infrared band of CH335Cl have been assigned. A root mean square (RMS) deviation of 0·020 cm-1has been achieved by a least-squares fit over 732 rovibrational lines of the perpendicular component; for this purpose, a model taking into account anharmonic resonances between (i) 2v4∓2andv4∓1+ 3v6∓1and (ii)v4∓1+ 3v6∓1and 6v6∓2was used. A RMS deviation of 0·018 cm-1has been achieved by a least-squares fit, according to an unperturbed model, of over 400 lines of the parallel component; many lines have been excluded from the fit because all theKsub-bands exhibit local anomalies.

ISSN:0026-8976    

DOI:10.1080/00268979300101591

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A Monte Carlo simulation scheme is developed to study thermal desorption of gas molecules from mixed adlayers containing two species where reactive and non-reactive desorption coexist. The effects of non-reactive desorption on the spectra of reactive desorption are investigated. The lateral interactions among adatoms, adsorbate islanding, surface diffusion, initial surface coverage and site energies are taken into account. It is observed that in a wide range, when the reaction energy of two species occupying adjacent sites is lower than the site energy of the old species, the non-reactive desorption has little or very limited effect on the spectrum of the reactive desorption, and only when the activation energy is quite close to the site energy of the old species does the non-reactive desorption affect the spectrum of reactive desorption, along with the initial coverage and the lateral interactions among adatoms. This indicates that earlier studies that separate reactive desorption from non-reactive desorption can be explained by the difference between the reaction energy and the site energies instead of the ‘time scale difference’ assumption. However, it is found that the non-reactive desorption terminates the reactive desorption earlier (cutting off the tail) in general cases and, when the non-reactive desorption is strongly effective, an increase of the coverage of B widens the spectrum of the reactive desorption instead of narrowing the spectrum, as in general cases, due to the effect of preventing early exhaust of the A species.

ISSN:0026-8976    

DOI:10.1080/00268979300101601

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in thev4(σu) antisymmetric stretch fundamental of the C6cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constantB0= 0·048 479 (10) cm-1and the effective bond lengthreff= 1·2868 (1) Å are in good agreement withab initiopredictions for the linear triplet (3Σ-g) state of C6.

ISSN:0026-8976    

DOI:10.1080/00268979300101611

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Formulae in terms of integrals and orbital energies are presented for the evaluation of the second-, third- and fourth-order energies in open-shell spinrestricted Møller-Plesset (RMP) perturbation theory. The performance of RMP theory is evaluated by calculating equilibrium structures and harmonic vibrational frequencies of a large number of open-shell systems and by calculating energies of reactions which have been shown to be poorly described by spinunrestricted Møller-Plesset (UMP) theory. RMP theory removes the spin contamination present in the unrestricted Hartree-Fock (UHF) reference of UMP theory. In cases where the spin contamination gives rise to large errors in UMP calculations, such as for the harmonic frequencies of NO, CN, CO+and FO2and the energies of reactions involving CN and FO2, RMP theory is shown to offer a substantial improvement. In cases where the Møller-Plesset series exhibits large oscillations, such as for O2, O+2and F+2, RMP theory is shown to offer no improvement over UMP theory; in these cases good results are achieved with higher-order methods such as quadratic configuration interaction and coupled-cluster theory.

ISSN:0026-8976    

DOI:10.1080/00268979300101621

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Outer sphere and inner sphere electron transfer reactions in the solvent of hard spheres with permanent dipoles are considered. The solvent reorganization energy has been shown to be the sum of the reorganization energy of reorientation of the permanent dipoles and the reorganization energy of changes in coordinates of solvent molecules. Analytical expressions for both contributions have been obtained. The free energy of activation appears to be temperature dependent, which can result in a negative activation enthalpy.

ISSN:0026-8976    

DOI:10.1080/00268979300101631

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor