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.     

关于在HIAF-BRing上开展自旋物理研究的提议(英文)

国家重大科技基础设施"强流重离子加速器装置"（High Intensity heavy-ion Accelerator Facility,HIAF）已由国家发改委批准立项并开始建设。建成之后,HIAF将为微观物质结构和重离子应用等研究提供很好的实验平台。HIAF的加速储存环（Booster Ring,BRing）设计可以加速最高动量为11.9 GeV/c的高流强质子束流。因此,HIAF-BRing将为GeV能区的核物理和强子物理研究带来新的机遇。另一方面,极化实验是研究微观物质及其相互作用的有力工具。我们提议启动相关物理和极化技术的预研工作,为在HIAF-BRing上开展自旋物理研究打下基础。The construction of the future scientific facility High Intensity heavy-ion Accelerator Facility (HIAF) in China has started. Once established, HIAF will provide excellent conditions for fundamental investigations on both matter structure and heavy-ion applications. The booster ring (BRing) of HIAF is designed to accelerate high-intensity protons with the maximum momentum of 11.9 GeV/c. Therefore it will bring new opportunities for the nuclear and hadron physics in the GeV region. Polarized experiments have been proved as a powerful tool in the explorations of the building blocks of matter. We propose to initiate a pre-investigation for the related physics and polarization techniques, which will lay the foundation of the spin physics at the HIAF-BRing.     

ChemInform Abstract: Study of the Geometrical Structure and the Vibrational Spectra of P4O8, P4O6S2, and P4O6Se2.

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.     

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.     

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.     

Intramolecular vibrational relaxation in aromatic molecules. 2: An experimental and computational study of pyrrole and triazine near the IVR threshold

The threshold region of vibrational energy redistribution (IVR) presents a great experimental and computational challenge for organic molecules with more than 10 degrees of freedom. The density of states ρ_tot is high and requires high resolution measurements over a wide range to cover all relevant timescales experimentally. Yet ρ_tot is sufficiently low that IVR quantities like the initial relaxation time τIVR or the number of participating states N_eff are very sensitive to the coupling structure. To highlight the competing effects of molecular symmetry and mode localization on the accessible density of states, this work complements a study of benzene (Callegari, A., Merker, U., Engels, P., Srivastava, H. K., Lehmann, K. K., and Scoles, G., 2000, J. chem. Phys., 113, 10583) by measuring the CH overtone spectra of pyrrole (C₄H₄NH) and 1,2,3-triazine (C₃N₃H₃) using eigenstate-resolved double-resonance spectroscopy. Large scale computations of IVR dynamics were undertaken, applying filter diagonalization to analytically fitted fourth-order ab initio force fields. With an overall adjustment to the anharmonicity of the potential, the modelled N_eff and τ_IVR agree with the experimental quantities within a factor of 2 to 3, which is reasonable for a rate theory in the threshold regime. The models also correctly predict the experimentally observed trends of τ_IVR and N_eff for the two molecules, and provide insight into the highly off-resonant coupling mechanism, which yields very sharp linewidths.     

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.     

ChemInform Abstract: Study of the P4O7, P4O6S,and P4O6Se Vibrational Spectra.

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: Relative Stability of the Planar and Butterfly-Like Structures of Cyclic P2O2.

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.