Ab initio calculations for propyne and the hydrogen bonded complex NH H C C CH 3 3

The hydrogen-bonded cluster NH₃ …H—C≡C—CH₃ has been investigated by means of the coupled electron pair approximation, making use of a basis set of 198 contracted Gaussian-type orbitals. The calculated equilibrium structure is r _1^e (N—H) = 1?0127 Å, α_e(∠HN…H) = 112?32°, R _1^e (N…H) = 2?3593 Å, r _2^e (acetylenic C—H) = 1?0690 Å, R _2^e (C≡C) = 1?2078 Å, R _3^e (C—C) = 1?4711 Å, r _3^e (C—H) = 1?0894 Å and β_e(∠CCH) = 110?50°. The recommended equilibrium dissociation energy is D _e = 12?4±0?5 kJ mol^-1 and the calculated equilibrium dipole moment is μ_e = – 1?468 D, with the positive end of the dipole at the ammonia protons. Harmonic wavenumbers and absolute infrared intensities for the totally symmetric modes are calculated. Compared with free propyne the acetylenic CH stretching vibration experiences a bathochromic shift of 93 cm^-1 and an intensity enhancement by a factor of 5?5.     

LIOUVILLE TYPE THEOREM FOR THE STATIONARY EQUATIONS OF MAGNETO-HYDRODYNAMICS

We show that any smooth solution(u, H) to the stationary equations of magnetohydrodynamics belonging to both spaces L~6(R~3) and BMO~(-1)(R~3) must be identically zero.This is an extension of previous results, all of which systematically required stronger integrability and the additional assumption ▽u, ▽H∈L~2(R~3), i.e., finite Dirichlet integral.     

CASSCF calculations of triplet state properties: applications to benzene derivatives

We illustrate the capability of the complete active space self-consistent field method by Roos and co-workers for calculations of triplet state properties. We report phosphorescence lifetimes, zero-field splitting parameters, and nuclear quadrupole coupling constants for the lowest triplet state of a variety of benzene derivatives.     

A Remark on Myberg Initial Data for Kleinian Groups

For a general Kleinian (N+1)-manifold, we consider the set of those initial data which give rise to trajectories reproducing the global canonical geodesic structure with arbitrary accuracy. We show that the positivity of the Patterson measure of this set is equivalent to the ergodicity of the geodesic flow on the manifold. This result allows us to generalize the Myrberg density theorem to Kleinian groups whose exponent of convergence exceeds N/2 and which are of -divergence Type.     

ChemInform Abstract: Singlet Diradical Character of S2N2.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

The LEDO expansion for diatomic overlap densities: application to the density functional theory of molecules

The limited expansion of differential overlap (LEDO) approach for the expansion of diatomic overlap densities in terms of mono-centre densities is discussed in the context of density functional theory (DFT). It is shown that it leads to a particularly simple construction scheme for major parts of the secular matrix, i.e. the electron-electron interaction and the exchange-correlation potential: using the LEDO expansion coefficients, matrix elements between atomic orbitals located on different centres can be expressed in terms of the corresponding mono-centre elements, thus allowing the reduction of three-centre and four-centre integrals to two-centre integrals. This results in the first DFT method with formal N ² scaling for the construction of the secular matrix, with N being the dimension of the atomic orbital (AO) basis set. Test calculations show that numerical agreement with the results of conventional DFT calculations is excellent.     

Theoretical investigation of the Renner-Teller effect in Δ electronic states of tetra-atomic molecules. 1. Variational calculation of vibronic structure in the 11Δg state of B2H2

A variational approach for the ab initio handling of the Renner-Teller effect in Δ electronic states of tetra-atomic molecules is presented. The model Hamiltonian involves four nuclear degrees of freedom which correlate for a linear nuclear arrangement with two doubly degenerate bending modes. The bond lengths are assumed to be kept fixed at their equilibrium values and the effect of end-over-end rotations is neglected. The kinetic energy operator and the general form of the potential surfaces employed allow in principle for a treatment of large amplitude bending vibrations. However, because of restrictions implied, such as neglect of coupling between bending and stretching vibrations and interactions with other electronic states, the approach is aimed primarily at molecules bending with relatively small amplitudes around their linear equilibrium geometries. Two algorithms are developed, one for symmetric acetylene-like (A-B-B-A) molecules, the other for asymmetric (A-B-C-D) species. The approach is applied to calculate the vibronic spectrum of the lowest lying excited state, ¹Δ_g, of B₂H₂, employing ab initio computed potential energy surfaces.     

Generation of high harmonics and attosecond pulses with ultrashort laser pulse filaments and conical waves

Results illustrating the nonlinear dynamics of ultrashort laser pulse filamentation in gases are presented, with particular emphasis on the filament properties useful for developing attosecond light sources. Two aspects of ultrashort pulse filaments are specifically discussed: (i) numerical simulation results on pulse self-compression by filamentation in a gas cell filled with noble gas. Measurements of high harmonics generated by the pulse extracted from the filament allows for the detection of intensity spikes and subcycle pulses generated within the filament. (ii) Simulation results on the spontaneous formation of conical wavepackets during filamentation in gases, which in turn can be used as efficient driving pulses for the generation of high harmonics and isolated attosecond pulses.     

ChemInform Abstract: Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride,FXe(N3), and Xenon Isocyanate Fluoride,FXe(NCO).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Electronically Excited States in Size Selected Solvated Alkali Metal Atoms. Part 1. First Observation in NaNH3 by Resonant Two Color Two Photon Ionization.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.