[en] The expressions used for describing the angular distribution of oriented and aligned reagent molecules are derived. The algebraic forms of orientation and alignment parameters of molecules in the excited states are obtained for two-photon excitation. The reagent molecules after absorbing two-photon may produce the higher order orientation and alignment than doing one-photon

[en] The photodissociation of m-bromotoluene at 266 nm has been investigated on the universal crossed molecular beam machine, and the time-of-flight (TOF) spectra of recoiling photofragment at different angles were measured with the photofragment translational spectroscopy (PTS) detecting technique. The observed TOF spectra indicate that there are two different dissociation channels, one is channel (A) β=0.7±0.1 and < E_t>=3.76±0.5 kcal/mol, the other is channel (B) β=0.2±0.15 and < E_t>=12.13±0.5 kcal/mol. To better interpret the experimental results and primary photodissociation mechanism, the ultraviolet-visible (UV) absorption spectra of m-, o- and p-bromotoluene were measured, and the geometries of m-bromotoluene were optimized at the CASSCF(8,7)/6-311G** level. Two probable photodissociation mechanisms are suggested based upon the experimental results and the ab initio calculation

[en] A three dimensional (3D) time-dependent wave-packet method has been used to solve the Schroedinger equation of an electron coupled with the nucleus. The re-collision probabilities between the electron and the D₂⁺ have been derived, and we find that most D₂⁺ ions come from the first re-collision between the electron and its parent ion D₂⁺ in the first optical period. Our calculation is in good agreement with experimental results. The quantum dynamics method to track the motion of both electron and nuclear wave packets with attosecond resolution is described. (authors)

[en] A theoretical investigation on the nonadiabatic processes of the full three-dimensional D⁺+H₂ and H⁺+D₂ reaction systems has been performed by using trajectory surface hopping (TSH) method based on the Zhu-Nakamura (ZN) theory. This ZN-TSH method refers to not only classically allowed hops but also classically forbidden hops. The potential energy surface constructed by Kamisaka et al. is employed in the calculation. A new iterative method is proposed to yield the two-dimensional seam surface from the topography of the adiabatic potential surfaces, in which the inconvenience of directly solving the first-order partial differential equation is avoided. The cross sections of these two systems are calculated for three competing channels of the reactive charge transfer, the nonreactive charge transfer, and the reactive noncharge transfer, for ground rovibrational state of H₂ or D₂. Also, this study provides reaction probabilities of these three processes for the total angular momentum J=0 and ground initial vibrational state of H₂ or D₂. The calculated results from ZN-TSH method are in good agreement with the exact quantum calculations and the experimental measurements

[en] The time-dependent-wave-packet method has been applied to calculate the kinetic energy distribution of H⁺ ion resulting from the recollision between the electron and its parent ion H₂⁺(X²Σ_g⁺) within subfemtosecond time scale. The recollision probabilities between the electron and H₂⁺ as a function of time have also been obtained. Also, an accurate quantum dynamics method has been applied to describe the motion of both the electron and the nuclear wave packets with attosecond resolution. The calculated results are in good agreement with experimental ones

[en] The photoisomerization mechanisms of bridged azobenzene are investigated by means of surface hopping dynamics simulations based on the Zhu-Nakamura theory. In the geometry optimizations and potential energy surface calculations, four minimum-energy conical intersections between the ground state and the lowest excited state are found to play important roles in the trans-cis and cis-trans isomerization processes. The trans-cis photoisomerization proceeds through two minimum-energy conical intersections. Ultrafast pedal motion of the N atoms and twisting of phenyl rings around their N–C bonds allows the molecule to move to a minimum-energy conical intersection, after which surface hopping from S₁ to S₀ occurs. In the S₀ state, further rotation occurs around the N=N bond and two N–C bonds until the azo moiety and phenyl rings complete their isomerization. Finally, the cis form is achieved by subsequent adjustment of the ethylene bridge. In the cis-trans photodynamics, there is one rotational pathway, in the middle of which two CIs are responsible for the surface hopping to the S₀ state. After the nonadiabatic transition, the molecule reaches the trans form through a barrierless pathway and the two phenyl rings and the additional bridge complete their reorientation almost at the same time.

[en] The effect of laser fields on the NO interaction potentials is obtained by the calculation of time-resolved photoelectron spectrum (TRPES) using the time-dependent wave-packet method. The calculation not only shows that the overlap of the pump-probe pulses makes some NO molecular 'invisible' states visible, but also that the coupling strength and the positions of relevant curves change on increasing the laser intensity. These changed potentials affect their dynamical behavior and influence the shape and position of each peak in TRPES. That the coupling strength of relevant potentials can be changed by the field-matter interaction is consistent with our ab initio calculations

[en] We present a method of producing single attosecond pulses by using a few-cycle (5 fs) driving pulse with two additional weak control pulses. We discuss how single attosecond pulses produced from high-order harmonic generation processes in a synthesized three-colour laser field are similar to those processes in a much shorter single-colour laser field. Based on the high-order harmonic spectrum, classical ionizing and returning energy maps, time-frequency maps and time profiles of the attosecond pulses, the actions of the synthesized three-colour laser field are analogous to a 3 fs field although some differences still exist, and our method is proved to be a potential way to reduce the attosecond pulse duration from high-order harmonic generation with a currently available ultrafast laser source instead of a shorter pulse.

[en] Highlights: • 3HF in methanol shows two ESPT rates corresponding to two hydrogen-bonded complexes. • The changes of energy barrier to the rate constant of ESPT of 3HF are in good agreement with Arrhenius equation. • The picosecond component in the decay of excited state of 3HF is induced by solvational dynamics. -- Abstract: 3-hydroxyflavone (3HF) has been found dual emission in polar and protic solvents for many years. The excited state proton transfer (ESPT) is the key to control the dual emissions of 3HF. We found the ESPT rate of 3HF in hexane is faster than in acetonitrile because of the lower ESPT energy barrier in hexane. Hence, it was found there are two ESPT rates in methanol, one is faster than in hexane, and the other is slower than in acetonitrile. Two solvent-solute hydrogen bonded complexes (I and II) response to the two ESPT rates. The energy barrier of ESPT was found the lowest (1.324 kcal/mol) in Complex I, corresponded to the shortest ESPT time constant (<0.09 ps). In Complex II, the ESPT time constant is the longest (21.97 ps) with the highest ESPT energy barrier (3.865 kcal/mol). Comparing the results of two complexes, we found that intermolecular hydrogen-bonds would accelerate or delay the ESPT of 3HF based on their different types.

[en] We demonstrated CdS quantum dot-sensitized solar cells (QDSSCs) based on anatase TiO₂ nanosheets with exposed {001} and {100} facets. Under the illumination of one Sun (AM 1.5 G, 100 mW cm⁻²), the photovoltaic conversion efficiencies were 2.29% for a QDSSC based on {001}-TiO₂ nanosheets, 2.18% for a QDSSC based on {100}-TiO₂ nanosheets, and 1.46% for a QDSSC based on commercial Degussa P25. It was found that the exposed highly reactive facets of TiO₂ nanosheets had a remarkable influence on the QDSSCs due to their better adsorption abilities for QDs, leading to the high short current density and the enhanced photovoltaic performance. (paper)