ISSN:0026-8976    

DOI:10.1080/00268970009483372

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

CI techniques, based on nearly complete expansions over determinants for subsets of molecular orbitals and electrons, have been extended to evaluate, by finite differences, non-adiabatic interactions arising from the nuclear kinetic energy operator. A functional of the non-adiabatic interactions is defined and, from the minimum condition of the functional, a simple expression is obtained for the transformation matrix to the quasi-diabatic basis. Two different schemes for the minimization of the functional, with and without constraints to the form of the transformation matrix, have been compared. Simple tests are presented to verify the numerical accuracy of the non-adiabatic interactions and to compare the two schemes for the minimization of the functional.

ISSN:0026-8976    

DOI:10.1080/00268970009483373

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A recently proposed[1999,J. chem. Phys., 111, 2401 and 1999,Chem. Phys. Lett., 312, 530] new semi-classical decoupling procedure for rotational projection states in ro-vibrationally inelastic atom-diatom and diatom-diatom collisions is applied to inelastic collisions in molecular hydrogen. The role of initial rotational excitation of both collision partners in the ro-vibrational transitions, attached to the vibrational (10 -> 00) transition in ortho-H2, is analysed in detail. The computed vibrational self-relaxation rate constant for ortho-H2(as earlier for para-H2, too) is in good quantitative agreement (within a factor of 2) with experimental data over the whole experimentally investigated temperature range, 50-3000 K. This also indicates that the more detailed (non-measured) rate constants for ro-vibrational state-to-state transitions in molecular hydrogen, calculated by our new model, are sufficiently accurate for astrophysical applications.

ISSN:0026-8976    

DOI:10.1080/00268970009483374

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A general method is presented for the evaluation of the spin rovibronic energy levels of triatomic molecules with up to three interacting potential energy surfaces. The full theory is outlined in detail, both for singlet and for doublet electronic states and the method is then applied to the benchmark example of C2H. High quality multireference configuration interaction calculations have been carried out to generate the 3-dimensional near-equilibrium adiabatic potential energy surfaces of the three lowest 12A'(X2Σ+), 22A'(A2Π), 12A''(A2Π) electronic states of C2H, and the pair of interacting states of A 0 symmetry have then been diabatized. Results are presented for J up to 7/2 and compared with gas-phase high resolution experimental results for energies up to 5600 cm1.

ISSN:0026-8976    

DOI:10.1080/00268970009483375

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The state specific predissociation of OH/OD in its lowest electronically excited state (A2Σ+,v',N',F1/F2) is investigated by time dependent wave packet propagation techniques. To improve the accuracy of the potential energy curves, spin-orbit, spin-spin and rotational interactions required for the treatment, we have refined our CI techniques, using optimal orbitals for each of the electronic states. Potential energy curves, matrix elements and lifetimes of the rotational sublevels are compared with experiment and with theoretical values from multichannel scattering theory

ISSN:0026-8976    

DOI:10.1080/00268970009483376

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Rate constants have been calculated using quasi-classical trajectories (QCT) for the vibrational relaxation of highly excited O2:O2(X3Σḡ,vi) + O2(X3Σḡ,0) → O2(X3Σḡ,vf) + O2(X3Σḡ) with 22 ≤vi≤28. The present full-dimensional QCT results agree very well with recent quantum reduced dimensionality calculations, giving further support to the hypothesis that the observed experimental jump in depletion rates would be due partially to enhanced vibrational relaxation.

ISSN:0026-8976    

DOI:10.1080/00268970009483377

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Anab initioquartic anharmonic force field for methanol has been calculated at the equilibrium position using the CCSD(T) method for the structure and the harmonic potential energy surface, and the MP4(SDQ) method for the anharmonic part of the surface. A triple zeta basis set was employed with symmetrized curvilinear internal valence coordinates in all calculations. The internal coordinate force field constants have been transformed into force constants in the dimensionless normal coordinate representation for various isotopomers. Vibrational term values for CH3OH, CH3OD, CD3OH, and CD3OD have been obtained using second order perturbation theory. Particular care has been devoted to the inclusion of Fermi resonance interactions between different vibrational states. A good accuracy has been achieved in the calculation of the fundamentals for all the isotopomers, the mean absolute error being 5.8 cm−1.

ISSN:0026-8976    

DOI:10.1080/00268970009483378

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A variety of phenomena of apparently different nature can be compacted and described within a unifying picture by taking into account the role of the charge transfer interaction. Relevant information on this interaction is obtained by the analysis of bond stabilization in halides, oxides, sulphides and ionic dimers of rare gases. Most of this information comes from recent molecular beam experiments: when combined with the analysis of processes occurring at crossings between covalent and ionic states in alkali halides it leads to the characterization of the dependence of the charge transfer matrix element on basic physical properties of the interacting partners. The magnitude of the coupling matrix element is correlated to polarizabilities and charges. Its exponential decreasing with intermolecular distance is given in terms of ionization potentials and electron affinities, in the spirit of the study by Grice and Herschbach (Molec. Phys., 1973,27, 159) on the long-range configuration interaction of ionic and covalent states. A proper representation is obtained both for the transition from van der Waals to chemical bonds and for the behaviour of different families of compounds, such as those of alkali halides and of rare-gas protonated systems.

ISSN:0026-8976    

DOI:10.1080/00268970009483379

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Forn-body dynamics an analysis is made of the properties of configuration space within a symmetric hyperspherical framework. Coordinates are conveniently broken up into spatial (or external) rotations, kinematic invariants (related to the inertia moments) and kinematic (or internal) rotations. Their usefulness is demonstrated for the study of constrained intramolecular motions and of concerted reactions and for collective modes of polyatomic molecules and clusters. For a fixed hyperradius, which is a measure of total inertia, the space of kinematic invariants is the surface of a right spherical triangle that leads to the tetrahedral (forn= 4) or octahedral (forn≥ 5) tessellation of the sphere. Alternative parametrizations are discussed, including the proper one to deal with the umbrella inversion motion of ammonia.

ISSN:0026-8976    

DOI:10.1080/00268970009483380

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Mixed quantum-classical calculations using propagation of 3D wavepackets in hyperspherical coordinates have been performed for the F + H2→ HF + H reaction using two different potential energy surfaces. Vibrationally resolved cross-sections show good agreement with those obtained from accurate quantum mechanical calculations.

ISSN:0026-8976    

DOI:10.1080/00268970009483381

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor