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Low-lying states of Ga2P and Ga2As are investigated with the equation-of-motion coupled-cluster approach for ionized states at the singles and doubles level (EOMIP-CCSD) as well as at the CCSDT-3 level together with CCSD, CCSD(T), and DFT. Except for the asymmetric stretching b2 mode of the 2B2 and 2A1 states, all these approaches provide structures, frequencies and adiabatic electron affinities that are in reasonable agreement with each other. According to our results, the lowest-energy state of these two molecules is the 2A′ state of Cs symmetry and the 2B2 state is the ground electronic state with C2v symmetry. As for the b2 mode, CCSD and CCSD(T) afford real frequencies for the 2B2 state, while EOM approaches and DFT with most exchange–correlation functionals give rise to imaginary frequencies. The 2B2 and 2A1 states couple with each other due to distortion along b2 mode through the pseudo-Jahn–Teller effect. Analysis on results shows that EOM approaches afford reasonable b2 frequencies for the two states and DFT approaches, except for BP86 and PBE, provide qualitatively correct b2 frequencies for the 2B2 state. In addition, a potential matrix is introduced to describe the vibronic coupling between the 2B2 and 2A1 states and parameters in the matrix are fitted to the adiabatic potential curves from EOMIP-CCSD results. [ABSTRACT FROM AUTHOR]

Abstract: Bis(7)-tacrine [bis(7)-tetrahydroaminacrine] is a dimeric AChE inhibitor derived from tacrine with a potential to treat Alzheimer''s disease. Actions of bis(7)-tacrine on ligand-gated ion channels and voltage-gated cation channels have been identified on neurons of both central and peripheral nervous systems. In the present study, the effect of bis(7)-tacrine was investigated on the KV4.2 encoded potassium currents expressed in Xenopus oocytes and the transient A-type potassium current (I K(A)) on rat DRG neurons. Bis(7)-tacrine suppressed recombinant Kv4.2 potassium channels in a concentration-dependent manner, with IC50 value of 0.53±0.13 μM. Tacrine also inhibited Kv4.2 channels, but with a much lower potency (IC50 74±15 μM).The possible mechanisms underlying the inhibition on potassium currents by bis(7)-tacrine/tacrine could be that inactivation of the transient potassium currents was accelerated and recovery of the native or Kv4.2 expressed potassium currents was suppressed by bis(7)-tacrine/tacrine. [Copyright &y& Elsevier]

Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge-balanced electron donor–acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor–acceptor complex was obtained by the second-order Møller–Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor–acceptor complex in this work reveals that the S1 and S2 states of the electron donor–acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S0 → S1 and S0 → S2 transitions arise from π–π* excitations. The charge recombination in the ion pair complex will produce the charge-balanced ground state or excited triplet state. According to the generalized Mulliken–Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2-dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23–35, 2003 [ABSTRACT FROM AUTHOR]

Based on the idea of damage control, a new type of earthquake-resilient prefabricated composite joint (ERPCJ) with the T-shape connector has been proposed. On the premise of considering the composite action of concrete slab and beam-column joint, the seismic behavior, post-earthquake recoverability and failure mode of concrete slab under different loading protocols are studied. By changing the connection mode between flange cover plate (FCP) and beam, the influence of the relative slip between FCP and beam on the bearing capacity and energy dissipation capacity of the specimen are also studied. The low frequency cyclic loading tests and low cyclic fatigue tests of six specimens show that the basic and repaired specimens of the prefabricated composite joints with recoverable functions show good seismic behavior. The plastic damage of steel joint is concentrated on FCP, while the main structural members such as beam and column still maintain elasticity. The collaborative work of T-shape connector with foams, concrete slab and the gaps between concrete slab and column can reduce the plastic damage of concrete slab. The main reason of concrete slab damage is the strong squeezing effect between concrete slab and T-shape connector in negative moment zone. Whether FCP can slip or not can make a great difference in the bearing capacity and energy dissipation capacity of the joint. The damage and deformation of FCP are small when FCP and beam can slide relatively, but the bearing capacity and energy dissipation capacity of the joint are low. The bearing capacity and energy dissipation capacity of the joint are high when FCP and the beam cannot slip relatively, but FCP will cause serious plastic damage and even fracture. [Display omitted] • An innovative prefabricated composite joint with T-shape connector was proposed. • Six quasi-static tests were designed and two connection modes were considered. • Seismic performance are studied under different loading protocols. • The damage to concrete slabs will be reduced by setting T-shape connector and gap. • Earlier FCP slip will reduce bearing capacity and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rate constants for hydrogen abstraction from quadricyclane were calculated by high-precision quantum chemical method. • Estimating the high-precision rate constants of the hydrogen abstraction from quadricyclane is risky. • Branching ratios are employed to explain the temperature dependence of rate constants. Hydrogen abstraction reactions play important roles in combustion process of fuel. In the present work, we carried out a comprehensive study on hydrogen abstraction from quadricyclane by seven radicals (H, O(3P), OH, CH 3 , HO 2 , C 2 H 5 , and CH 3 O). Geometry optimization and frequency calculations of all species are performed employing BH&HLYP/6-311++G(d,p) and single point energies are computed at CCSD(T)/CBS(D-T) level. High-pressure-limit rate constants for 21 elementary reactions are determined varying from 500 to 2500 K according to the conventional transition-state theory and represented with the modified Arrhenius form. Base on barrier heights, OH radical has the highest reactivity among the seven radicals and the H atom located at the secondary site is the easiest to be abstracted. The apparent discrepancies of rate parameters between our calculated results and the values taken from literatures indicate that present quantum chemical calculations are valuable and contribute to the future construction of combustion mechanism of quadricyclane. [ABSTRACT FROM AUTHOR]

• Systematic theoretical study on allylic hydrogen abstraction by HO 2 radical. • Reaction reactivity: primary hydrogen < secondary hydrogen < tertiary hydrogen. • Differences of rate constants between alkanes and alkenes are quite large. • Obtained rate rules is applicable to similar reactions in mechanism construction. Hydrogen abstraction reaction from allylic sites by HO 2 radical is important in the ignition chemistry of alkenes. A systematic study with a series of C 4 -C 7 alkenes as reactants is performed in present work to obtain the rate rules for the reaction class using G4 method coupled with transition state theory. The size and chain length of substituent groups and the configuration of reactant have little effect on the rate constants within a class. Hence, the rate rules are concluded by taking the average of the rate constants of a representative set of reactions. The reactivity for both alkenes and alkanes are similar with tertiary hydrogen possessing the highest activity and primary hydrogen possessing the lowest activity. The rate constants of alkanes and alkenes for these reaction classes are quite different at low temperatures. The obtained rate rules are applicable to the similar reaction classes of larger alkenes and alkanes. [ABSTRACT FROM AUTHOR]

Hydrogen abstraction from carbonyl-hydroperoxide is a new reaction class in the low-temperature oxidation of hydrocarbons. In this work, a comprehensive study to the kinetics for the hydrogen abstraction from cyclohexane-carbonyl-hydroperoxide (CCHP) is investigated using the CBS-QB3 composite method. Five small active radicals (H, CH3, O (3P), OH and HO2) are selected as the extracting agents, and the corresponding barrier heights are computed. Guided by the reaction barriers, the preferable path on hydrogen abstraction from CCHP is identified. The two-transition-state model is employed to obtain the overall rate constant when HO2 and OH act as the extracting agents due to the formation of reactant and product complexes. High-pressure-limit rate constants for 25 elementary reactions are reported in the modified Arrhenius form. Branching ratios for the site-specific hydrogen abstraction reactions ranging from 300 to 2500 K are illustrated to show the temperature dependence of preferable path. Compared with the theoretical rate constants obtained in this work, the values estimated by using analogy rules have obvious deviations at low temperature. The obtained hydrogen abstraction reactions are added to the JetSurF2.0 mechanism, thereby improving its kinetic modeling results for cyclohexane oxidation. Present work provides accurate kinetic parameters for this new type of reaction class which can be helpful to improve the predictive capability for hydrocarbon mechanism. [ABSTRACT FROM AUTHOR]

lthough vinyl alcohol(CH=CHOH)molecule was found to be an important intermediate in the combustion flames of hydrocarbon (Taatjes et al. in Science 308:1887, ), the removal mechanism of vinyl alcohol has not been established yet. The removal mechanism is critical to characterize the kinetics behavior of hydrocarbon in combustion chemistry and to develop the chemical models of hydrocarbon oxidation. In this work, the potential energy surface for the unimolecular decomposition of syn-CH=CHOH reaction has been first studied by ab initio. The kinetics and product branching ratios for the decomposition reaction are evaluated by Variflex code in the temperature range of 500-3,000 K at 0.1, 1.0, and 100.0 atmosphere pressure. The results show that the formation of CH + CHO via the CHCHO intermediate is dominant in the decomposition reaction and its branching ratios at 0.1, 1.0, and 100.0 atm are more than 99.90, 99.30, and 89.20%, respectively, through the whole temperature range investigated. [ABSTRACT FROM AUTHOR]

Abstract: The electron transfer of a model system, Au-benzene-1,4-dithiolate-Au, in the presence of an external electric field is investigated. Both the cis- and trans-conformations are considered. The calculations show that, for both conformations, the interatomic distance between gold and sulfur on the site with an extra localized electron is shortened by about 0.17Å when the extra electron transfers to the other site. On the other hand, the reorganization energies of both conformations are almost the same, about 29kJmol−1. The electron transfer coupling matrix elements are 0.42 and 0.73kJmol−1, while the threshold field strengths are 8.5×10−4 and 7.4×10−4 a.u. for the cis- and trans-conformations, respectively. [Copyright &y& Elsevier]