摘要:

Kinematic rotations for four body processes canbe conveniently represented as arcs connecting the different reactive rearrangements, (T + UVW, TU + VW, TUV + W and all permutations). The arcs can be considered as forming great circles on a sphere, which is therefore a convenient manifold for setting up symmetric coordinates in asymptotic rearrangement channels: in the particular cases where the reactions are collinearly dominated, the sphere provides the full chart for the (fixed moment of inertia or hyperradial) mapping of the potential energy surface. Also,the representations can be extended to include connections to a formulation where two particles are symmetrically treated with respect to a third one-as introduced in the Journal of Chemical Physics (1986, 85, 1355)-and to encompass the asymptotic situation of the four body system decomposing into three fragments (T + U + VW, T + UV + W, etc...). Comments are made on other cases pertaining to the symmetric parametrizations of four centre processes.

ISSN:0026-8976    

DOI:10.1080/002689796173976

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The InO molecule has been produced in a molecular beam using a laser vaporization source, and its (0,0) band, near 428.2 nm, has been studied by laser-induced fluorescence at sub-Doppler (~0.005 cm-1) resolution. The spectrum is characterized by impressive nuclear magnetic hyperfine structure due to the 11.5 In nucleus. Analysis ofthe rotational and hyper fine structure in the band indicates that the transition is B2Sigma+ (case b beta s) - X2 Sigma+ (case b beta J) in which there is a large hyperfine splitting in the upper state and a predominantly spin-rotation splitting in the lower (ground) state of the molecule. The band origin, nu(0,0), lies at 23332.296 cm-1, and derived constants, in cm-1, for the two v = 0 levels are as follows: (table omitted) Dispersed fluorescence experiments and photographic emission spectroscopy using microwave excitation, hollow cathode and dc arc sources have been employed to obtain vibrational data.

ISSN:0026-8976    

DOI:10.1080/002689796173985

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A further parallel between the planar [18]annulene and benzene has been demonstrated: the existence of a topologically equivalent S0/S1 conical intersection. The lowest energy point on the crossing has been optimized with the MMBV and CASSCF+GVB/4-31G methods. These calculations suggest that fluorescence might be observed from the S1 state of [18]annulene, and that this would disappear at higher vibrational excess energies as a route to efficient non-radiative decay via the conical intersection became accessible (the 'channel 3' mechanism for benzene).

ISSN:0026-8976    

DOI:10.1080/002689796173994

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Ab initio calculations at the MP2/6-31+G(d,p) level of theory have been carried out to determine the equilibrium structures and vibrational spectra of three series of complexes involving the hydrogen halides HF, HCl, and HBr, and a set of 4-substituted pyridines. The hydrogen bonds in these complexes span the range of hydrogen bonding possibilities, including traditional Y-H...N, proton-shared Y...H...N, and ionic Y-...H+-N hydrogen bonds. The type of hydrogen bond in a complex is related to the proton affinity of the substituted pyridine and the nature of the hydrogen halide. Plots of normalized distance and force constant changes versus the proton affinity of the substituted pyridines exhibit breaks which correlate with the three types of hydrogen bond. The infrared spectra of all complexes exhibit very intense bands associated with motion of the hydrogen-bonded proton along the Y-N axis. The shift to lower frequency of this band in complexes with traditional hydrogen bonds increases as the proton affinity of the substituted pyridine increases. A shift of greater than 40% relative to the free HY frequency is a spectroscopic signal of the presence of a proton-shared hydrogen bond.

ISSN:0026-8976    

DOI:10.1080/002689796174001

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

New expressions are developed within the electric dipole approximation for the four Stokes parameters characterizing the polarization properties of coherent second-harmonic radiation generated from chiral isotropic surfaces in reflection. These are employed to derive, in addition to the three well-known incident circular polarization second-harmonic opticalactivity (SHOA) observables, thirteen new basic observables for the detection of surface SHOA which involve second-harmonic intensity difference measurements using right and left circular, and + 45 and - 45 linear, polarization modulation in the incident and second-harmonic radiation and in both simultaneously. Because of their dependence on a fully electric dipole allowed tensor these circular and linear intensity differences and the corresponding intensity sums have the same order of magnitude, so that all the dimensionless surface SHOA effects they generate are of the order of unity. The circular intensity differences (CIDs) depend on the imaginary part of products of second-order surface susceptibility tensor components and can therefore be observed only under preresonance or resonance scattering conditions; whereas the linear intensity differences (LIDs) depend on the real part of the same tensor component products and can therefore also be detected at transparent frequencies. Employing elliptically polarized incident radiation, appropriate combinations of CIDs and LIDs also measure, respectively, real and imaginary parts of the relevant surface susceptibility tensor products so that a suitable CID combination may also be detected under non-resonance scattering conditions. The best experimental strategies are identified for SHOA detection and extraction of complete SHOA information and relationships are discussed between the SHOA observables and the second-harmonic polarization azimuth, ellipticity and degree of polarization. Because only pure electric dipole scattering processes are considered, the basic formalism applies also to magnetically induced SHOA phenomena.

ISSN:0026-8976    

DOI:10.1080/002689796174010

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A symmetry-adapted perturbation theory (SAPT) is formulated for interaction-induced electrical properties of weakly bound complexes. Asymptotic (large R) expressions are reported for the contributions to the collision-induced dipole moments and polarizabilities up to and including second order in the intermolecular potential. These long-range expressions require knowledge only of the multipole moments and (hyper)polarizabilities of the isolated monomers. Numerical results are given for the dipole moment of He-H2 and the polarizability of He2 and the accuracy of the SAPT approach is examined by comparison with full configuration interaction results. The role of various physical contributions to the dipole moment of He-H2 and the polarizability of He2 is investigated. The validity of the long-range approximation and the importance of charge penetration (damping) effects are discussed.

ISSN:0026-8976    

DOI:10.1080/002689796174029

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A unified review of various Kohn variational methods for scattering calculations is presented using appropriate Bloch operators. Previous expressions are generalized slightly to use either an infinite range or a finite range of the scattering coordinate, or to use a basis set with non-fixed log derivative boundary conditions. A non-variational method (method of moments) is used in the derivations; the results are confirmed by Kohn variational derivations. Speculative linear variation functionals are introduced to connect both derivations. A model calculation of K (reactance) matrix is presented using a finite range and real algebra which is free of the so called 'Kohn anomaly', unlike the conventional Kohn method for the K matrix.

ISSN:0026-8976    

DOI:10.1080/002689796174038

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The electric field gradients at the halogen nuclei in hydrogen halides are calculated by using the coupled cluster method for the treatment of the electron correlation, and the spin-averaged no-pair approximation for the evaluation of the relativistic contribution. Upon combining these results with microwave spectroscopic data for nuclear quadrupole coupling constants in HCl, HBr, and HI, the following values of the nuclear quadrupole moment of the halide nuclei are obtained: Q(35Cl) = 0.0816 barn, Q(79Br) = 0.2989 barn, and Q(127I) -0.651 barn. The present 'molecular' value of Q(35Cl) agrees with the latest 'atomic' data. The results obtained for 79Br and 127I strongly indicate that the current recommended standard values of their nuclear quadrupole moments need to be revised.

ISSN:0026-8976    

DOI:10.1080/002689796174047

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Relativistic and non-relativistic all-electron, ab initio methods are used to investigate the role of the individual energy components in the total interaction energy involved in the formation of the weakly bound ground state X1Sigma+g of the Hg2 molecule. The interaction energy is partitioned according to a hybrid approach into a supermolecular repulsive potential and the damped dispersion energy derived from perturbation theory. Both parts are then computed individually and their dependence on relativity and electron correlation investigated. From this analysis, hybrid potentials that comprise different physical interactions are constructed and the importance of specific features is evaluated by comparison of the appropriate hybrid potentials with each other and with the experimental curve. The most detailed model is based on a CASSCF supermolecular potential to which the damped intramonomer correlated dispersion energy series is added. In the relativistic case it yields a potential with quantitatively correct asymptotic behaviour and which is able to predict potential parameters that agree reasonably well with the experimental results.The asymptotic density method developed by Duman and Smirnow was tested as an inexpensive alternative for the calculation of the repulsive part of the hybrid potential. In spite of its recent success in the calculation ofthe He-He potential, it cannot provide a good repulsive component in the case of Hg2. As a result of this work, this failure can be attributed to the unusually strong induction effects in the ground state mercury dimer bond, which lower repulsive forces substantially.

ISSN:0026-8976    

DOI:10.1080/002689796174056

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A theoretical method is presented for determining molecular hypermagnetizabilities and magnetic shielding polarizabilities to first order in a perturbing electric field. The procedure is based on formal annihilation of either diamagnetic or paramagnetic contributions to the quantum mechanical electron current density, via a continuous transformation of its origin all over the molecular domain. Analytical expressions for the third-rank tensors are obtained, which, in the limit of exact eigenfunctions to a model Hamiltonian, reduce to the conventional terms. They can also be expressed as the expectation value of certain commutators over the reference electronic state. In any calculation relying on the algebraic approximation, irrespective of size and quality of the (gaugeless) basis set employed, all the components of the magnetic shielding polarizability evaluated within these methods are origin independent, and the constraints for charge and current conservation are exactly satisfied. On the other hand, the hypermagnetizability depends linearly on the origin of the vector potential.

ISSN:0026-8976    

DOI:10.1080/002689796174065

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor