摘要:

In a recent paper (1986,Molec. Phys.,59,985), it was shown that rotational correlation functions of N2O dissolved in SF6may be reproduced using a simulated two Lennard-Jones centre liquid model. Our simulations provided an explanation of why simple theoretical models fail to describe the rotational motion. Following the same method, we investigate, in this paper, the models based on the memory function formulation. The main conclusions are that one of the models is particularly well adapted for the low reduced torque cases (≃16) while another is good for the high reduced torque cases (≃74). The simulated reduced torque range (20–50) corresponding to our experimental data lies precisely between these limits. This explains why the system N2O/SF6was not correctly approximated by usual memory function models.

ISSN:0026-8976    

DOI:10.1080/00268978700102961

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The ground state potential energy curves of alkaline-earth monohydride ions have been investigated. A pseudopotential formalism including a corepolarization potential has been used. For the valence correlation energy a local spin density functional with corrections for self interaction has been employed. Dissociation energies, bond lengths and vibrational frequencies are reported, and so are the vertical and adiabatic ionization potentials of the alkali and alkaline-earth monohydrides, which were obtained using the same theoretical model. A discussion and a comparison with other values, both theoretical and experimental, are also included.

ISSN:0026-8976    

DOI:10.1080/00268978700102971

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Emission in the spectral region 300–900 nm has been observed following 193 nm excimer laser photolysis of N2H4and N2D4. Electronically-excited NH(A) and ND(A) are formed by a two photon process with rotational and vibrational distributions that can be characterized by a single temperature of ∼ 4000 K and ∼ 3800 K, respectively. The visible spectrum in the region 420–900 nm shows a broad and largely unstructured continuum emission upon which is superimposed a large number of well-resolved spectral features corresponding to NH2(Ã) (or ND2(Ã)). This emission is formed by a single photon process that is essentially synchronous with the laser pulse and it is suggested that NH*2is formed directly by cleavage of the N-N bond in hydrazine. The visible emission is found to show two lifetimes; one of ∼ 25 μs and the other in excess of 100 μs, depending whether the measurement is performed on discrete spectral features or on the total emission. It is suggested that the longer component is associated with the continuum emission and possibly results from a Renner-Teller coupling of the excited NH2(Ã,2A1) state with high vibrational levels of the ground state, NH2([Xtilde],2B1). Experiments with various buffer gases show that for the high vibrational levels of the NH*2populated, vibrational relaxation of the NH*2takes place on a timescale that is comparable to electronic quenching.

ISSN:0026-8976    

DOI:10.1080/00268978700102981

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Studies on the ‘single particle’ (infrared) and collective (far-infrared and microwave) reorientational motions of benzonitrile liquid have shown that rotation is relatively slow. The static and dynamic total dipole correlations are sensibly described by the Glarum-Powles relationship between collective and single molecule times. These correlations include (at least) a contribution from short-ranged potentials. The total dipole density correlation function is successfully described by the Lynden-Bell/Steele gaussian cage model for libration in quasi-static cages but with parameters which predict intermolecular torques smaller than for more rapidly rotating liquid phase molecules. There is also some indication of a time scale separation between collective reorientational and interaction-induced dipole fluctuations.

ISSN:0026-8976    

DOI:10.1080/00268978700102991

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The vibronic structure of the 11Π ←XΣ+electronic transition in HCN and DCN is studied by means ofab initiomethods. The positions and intensities of corresponding spectral bands are predicted and the results of these calculations lead to a new interpretation of experimental findings concerning theC←XandD←Xspectra of HCN and DCN.

ISSN:0026-8976    

DOI:10.1080/00268978700103001

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Electronic ground state and lowest lying excited singlet species of predominantly valence character of acetylene are studied by means of theab initiomethod. The potential curves are calculated for trans- and cis-bending, symmetric C-H and C-C stretching vibrations at planar molecular geometries and for torsional motion at a number of values of the H-C-C bond angle. It is found that the electronic species studied are contaminated at non-linear and non-planar nuclear arrangements with Rydberg-type configurations. A very simple vibrational analysis of the electronic transitions 11Σ-u← 11Σ+gand 11Δu← 11Σ+g(D∞hnotation), neglecting all types of mode couplings (vibrational and vibronic, i.e. non-adiabatic), is performed. The results obtained are employed for an interpretation of the observedÃ←[Xtilde]and[Btilde]←[Xtilde]spectra of acetylene.

ISSN:0026-8976    

DOI:10.1080/00268978700103011

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In 1920 Max Born described the coupling of the intrinsic molecular spin to the hydrodynamic vorticity. At small shear rates molecules rotate at an angular velocity ⟨ω⟩ = ½∇ × u. In this paper we report the results of NEMD simulations which show that outside the linear regime, the average angular velocity ⟨ω⟩ is less than 1/2y.

ISSN:0026-8976    

DOI:10.1080/00268978700103021

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The technique of laser induced detection of chemical reaction products has been used to study the reaction: I2+ F → IF + I. Using a single frequency dye laser and an accurate wavenumber measurement, theX1Σ+→B3Π(0+) excitation spectrum of the product IF molecules has been studied with high resolution over a large spectral range (700–789 nm and 837–873 nm). Due to the exoenergicity of the reaction very high rovibrational levels are populated in theXstate up to ν″ = 20. Our measurements, together with those of previous authors, have allowed us to obtain an improved and extended spectroscopic representation of theXandBstates of IF in terms of Dunham coefficients.

ISSN:0026-8976    

DOI:10.1080/00268978700103031

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The radiative lifetimes of thea1Δ andb1Σ+states in SeO have been evaluated by perturbation expansions including a large number of states represented by extensive MRD-CI wavefunctions up to 7000 selected configurations each; the AO basis set contains 94 gaussians up toffunctions. The mixing coefficients are obtained from the spin-orbit operator in the Breit-Pauli form evaluating all one- and two-particle terms explicitly. Relativistic corrections to the kinetic and one-electron potential term in the zero-order hamiltonian are shown to be quite effective for the proper description of the spin-orbit terms. The radiative lifetime of theb1Σ+state is calculated to be determined in the main by the perpendicularb1Σ+-X3Σ±1/-transition which is about 2 times stronger than the parallel component. The calculated radiative lifetime of τ = 4·7ms is to compare with the recently measured τ = 1·4ms. The calculations predict τ = 1·1s for thea1Δ state. The magnetic dipole transitionsb-xanda-xwhich have experimentally been observed for the SeS but not yet for the SeO system is also calculated and the calculations predict τ = 230 ms for the perpendicular magnetic dipole transitionb1Σ+-X3Σ-. They analyse the various transition mechanisms and suggest that the theoretical treatment so far applied for molecules containing first- and second-row atoms can be extended with slight modification to heavier systems such as SeO in which the spin-orbit interaction is substantial.

ISSN:0026-8976    

DOI:10.1080/00268978700103041

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The potential energy surface of HeH2/+is used to illustrate the factors that arise when there is degeneracy in the electronic states of the charged fragments at dissociation limits. At short H-H distances the positive charge is shared equally between the two atoms. At large H-H distances, but one short H-He distance, the charge resides on one of the hydrogen atoms. These limits and intermediate situations, affect the induction and dispersion contributions on the HeH2/+potential energy surface.

ISSN:0026-8976    

DOI:10.1080/00268978700103051

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor