Search

A semiempirical theoretical model is developed for estimating the rates of collision-induced V-T vibrational relaxation. The model is useful for estimating the absolute magnitude of state-to-field vibrational relaxation rate coefficients within an overall accuracy of thirty percent and with an average error of -10 percent.

The reaction of OH with acetaldehyde in the gas phase is studied by tunable infrared laser kinetic spectroscopy. The major product of the reaction, CH3CO, reacts with O3 producing CH3, CO2 and O2 in one channel and producing CH3CO2 and O2 in the other channel.

A variety of rotational-level population distributions are prepared in the 6(super 1) vibrational level of (super 1)B(sub 2u) benzene, and the rotational distributions within 0 degree that result from collisions with H2, D2, or CH4 are observed. The 0 degree distributions for D2 are broader than for H2, illustrating that the reduced mass and rotational-level spacings play an important role in determining the rotational changes that occur.

The low temperatures and high resolution associated with helium droplet spectroscopy are used to obtain vibrational spectra for clusters containing a single HF molecule. The results suggest that, for n=9 and larger, the solvent cage becomes highly isotropic allowing the HF molecule to undergo nearly free rotation.

The picosecond molecular dynamics in an artificial bacteriorhodopsin (BR) pigment, BR6.11, are measured by picosecond time-resolved coherent anti-Stokes Raman spectroscopy (PTR/CARS) and picosecond transient absorption (PTA). The changes in the vibrational degrees of freedom of the retinal attributable to the six-membered carbon ring are found in the picosecond resonance CARS (PR/CARS) spectrum of ground-state BR6.11.

The microscopic solvation effect on the intramolecular charge-transfer (ICT) reaction of (p-cyanophenyl)pentamethyldisilane (CPDS) was observed in supersonic jets. Two significant microscopic solvation effects were observed that are an increase in the Stokes shift and an acceleration of the ICT process.

Three distortion modes, trans and cis bending and twisting, of ethylene, disilene, and digermene and their anions are discussed in terms of a generalized π–σ* orbital mixing model using PMO theory. The model predicts that trans- and cis-bent geometries of neutral dimetallenes may be stabilized from the planar geometry but with very small energy gains and that these geometries should be largely stabilized with significant bend angles and stabilization energies in dimetallene anions. Twisting around the double bonds of dimetallenes may lower the energy of the anions. The above prediction is verified by the potential energy surface calculations at the B3LYP/6-311++G(3df,3pd) level. [ABSTRACT FROM AUTHOR]

Ethynylsilyllithiums R1R2(R3CC)SiLi:  R1R2t-BuMe2Si, R3Me3Si (5a); R1R2t-BuMe2Si, R3Ph (5b); R1R2R3Me3Si (5c); R1t-BuMe2Si, R2Ph, R3Me3Si (5d); R1t-BuMe2Si, R2Me3SiCC, R3Me3Si (5e) were prepared by the sila-metalation reactions of the corresponding hydrosilanes using tert-butyllithium in THF and trapped by MeI, Me3SiCl, and i-Pr3SiCl in high yields. X-ray structural analysis of a single crystal of 5ahas revealed that 5aadopts a dimer form (7a) containing one THF molecule per dimer. Dimer 7ais a syn dimer with a planar four-membered ring made by two lithium atoms and two anionic silicon atoms; one lithium atom is coordinated by two ethynyl groups and the other by a THF molecule, indicative of the importance of the coordination of ethynyl groups for the stabilization of the silyllithium. 7Li NMR analysis indicates that the dimeric structure of 5a(7a) is maintained in toluene, but 5ais monomeric in THF. Rates and activation parameters of facile intramolecular exchange of the two lithium atoms in 7aobserved in toluene-d8were determined by the dynamic 7Li NMR. The DFT calculations of a model ethynylsilyllithium (H3Si)2(H3SiCC)SiLi, 12have shown that dimer 13, with a similar geometry to 7a, is more stable than the monomeric form. The optimized monomeric form of 12(12‘) has an ethynylsilyllithium-type structure with a largely bent Si−CC skeleton, suggesting significant intramolecular coordination to Li. [ABSTRACT FROM AUTHOR]