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[en] The Roothaan expression for the energy of a closed-shell molecular system is generalized in order to apply to open shells. A continuous variation from 0 to 2 is supposed for each level's occupation number, extending to this range tbe correction due to the spurious repulsion appearing in the half-electron method. The characteristic equations of the Xα method are applied to the energy expressions. The one level case is discussed in detail. Ionic and excited states of the 1,3 transbutadiene π system are analyzed
[en] The reaction mechanisms forming lithio silole, 2, from silyl 1,4-dilithio 1,3-butadiene, 1, were examinedtheoreticall y at the CCSD/6-31+G(d)//B3LYP/6-31+G(d) level of theory in the gas phase. To account forthe solvent effects, the reactions in diethyl ether were examined using the polarizable continuum model of the integral equation formalism (IEFPCM) with the united atom topological (UA0) cavity model at the IEFPCM-CCSD/6-31+G(d)//IEFPCM-B3LYP/6-31+G(d) level of theory. Without hexamethyl-phosphoramide (HMPA) as a cosolvent, the lithio silole, 2, was not produced due to the higher activation bar-rier, which is comparable to the homolytic cleavage of CC and/or C S bonds. On the other hand, the reaction could be feasible if HMPA solvates strongly or dissociates two Li+cations from the reaction system. This sug-gests that HMPA plays a decisive role in the reaction. The optimized structures of the stationary point species on the potential energy surfaces in diethyl ether were similar to those in the gas phase, suggesting that the solvent effects on the structures of stationary species were not so large. On the other hand, the ΔE_ZPVE"≠ values in diethylether showed larger changes from the corresponding values in the gas phase.
[en] Ion-molecule reactions of C3H+4 with C3H4 in cyclopropene/propyne and allene/propyne mixtures as well as in pure cyclopropene and allene are studied by a photoionization mass spectrometer. Product distributions of C3H+3, C6H+5, and C6H+7 differ in intensity from one system to another. Such differences are attributed to the nature of reactants and intermediates. The structure of the neutral molecule is especially significant in determining the product distribution. (orig.)
[en] The strong field ionization rates for ethylene, trans 1,3-butadiene, and trans,trans 1,3,5-hexatriene have been calculated using time-dependent configuration interaction with single excitations and a complex absorbing potential (TDCIS-CAP). The calculations used the aug-cc-pVTZ basis set with a large set of diffuse functions (3 s, 2 p, 3 d, and 1 f) on each atom. The absorbing boundary was placed 3.5 times the van der Waals radius from each atom. The simulations employed a seven-cycle cosine squared pulse with a wavelength of 800 nm. Ionization rates were calculated for intensities ranging from 0.3 × 1014 W/cm2 to 3.5 × 1014 W/cm2. Ionization rates along the molecular axis increased markedly with increasing conjugation length. By contrast, ionization rates perpendicular to the molecular axis were almost independent of the conjugation length
[en] In this paper, we report theoretical electron impact ionization cross sections from threshold to 2000 eV for isocarbonic open chain molecules C4H6, C4H8, C4F6 including their isomers, and closed chain molecules c-C4H8 and c-C4F8. Theoretical formalism employed presently, viz., Complex Scattering Potential-ionization contribution method has been used successfully for a variety of polyatomic molecules. The present ionization calculations are very important since results available for the studied targets are either scarce or none. Our work affords comparison of C4 containing hydrocarbon versus fluorocarbon molecules. Comparisons of the present ionization cross sections are made wherever possible, and new ionization data are also presented
[en] We report measured and calculated differential elastic cross sections for collisions of low-energy electrons with diacetylene (1,3-butadiyne). A generally satisfactory agreement between theory and experiment has been found. The calculated cross sections provide interesting insight into the underlying resonant structure.