含时波包动力学方法研究飞秒激光场下NH3分子通过中间预解离态A^～的光电子能谱

本首次利用二维含时波包动力学理论研究了飞秒激光场下NH3分子通过中间预解离态A^～的共振增强多光子电离光电子能谱(REMPI—PES)，得到了与实验相同的结果。计算中应用多项式函数拟合从头算结果得到的内坐标下的二维解析势能面包括基态X^-、中间预解离态A^～以及其它准连续的电子-离子对态，并经坐标变换得到质量加权坐标系下的相应势能面。劈裂算符-快速傅立叶变换(FFT)方法是波包传播的基本方法。计算分析表明，脉冲的形状(强度、脉宽等)对光电子能谱有着很大的影响，能谱中的三组峰簇可以认为是由强场对势能面的影响引起的，因而强场效应是解释飞秒时间分辨光电子能谱的关键。这种思想对实现原子和分子过程的相干控制具有重要的意义。     

Accurate ab initio-based analytical potential energy function for S_2(~1△_g) via extrapolation to the complete basis set limit

The potential energy curves(PECs)of the first electronic excited state of S_2(~1△_g) are calculated employing a multi-reference configuration interaction method with the Davidson correction in combination with a series of correlationconsistent basis sets from Dunning:aug-cc-p VX Z(X=T,Q,5,6).In order to obtain PECs with high accuracy,PECs calculated with aug-cc-p V(Q,5)Z basis sets are extrapolated to the complete basis set limit.The resulting PECs are then fitted to the analytical potential energy function(APEF)using the extended Hartree–Fock approximate correlation energy method.By utilizing the fitted APEF,accurate and reliable spectroscopic parameters are obtained,which are consistent with both experimental and theoretical results.By solving the Schr o¨dinger equation numerically with the APEFs obtained at the AV6Z and the extrapolated AV(Q,5)Z level of theory,we calculate the complete set of vibrational levels,classical turning points,inertial rotation and centrifugal distortion constants.     

Dynamics of molecular alignment steered by a few-cycle terahertz laser pulse

The field-free alignment of molecule ClCN is investigated by using a terahertz few-cycle pulse (THz FCP) based on the time-dependent density matrix theory. It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCPs in the adiabatic regime and the non-adiabatic regime. The matching number can affect both the maximum value of the alignment and the time at which it is achieved. It is also found that a higher degree of alignment can be achieved by using the THz FCP at lower intensity and there exists an optimal threshold of molecular alignment with the increase of the field amplitude. Also found is the frequency sensitive region in which the degree of maximum alignment can be enhanced greatly by modulating the center frequencies of different THz FCPs. The investigation demonstrates that comparing with a THz single-cycle pulse, a better result of the field-free alignment can be created by a THz FCP at a constant rotational temperature of molecule.     

Manifestation of external field effect in time-resolved photo-dissociation dynamics of LiF

The photo-dissociation dynamics of LiF is investigated with newly constructed accurate ab initio potential energy curves (PECs) using the time-dependent quantum wave packet method. The oscillations and decay of the wave packet on the adiabats as a function of time are given, which can be compared with the femtosecond transition-state (FTS) spectroscopy. The photo-absorption spectra and the kinetic-energy distribution of the dissociation fragments, which can exhibit the vibration-level structure and the dispersion of the wave packet, respectively, are also obtained. The investigation shows a blue shift of the band center for the photo-absorption spectrum and multiple peaks in the kinetic-energy spectrum with increasing laser intensity, which can be attributed to external field effects. By analyzing the oscillations of the wave packet evolving on the upper adiabat, an approximate inversion scheme is devised to roughly deduce its shape.     

Symmetrical adhesion of two cylindrical colloids to a tubular membrane

With the full treatment of the Helfrich model we theoretically study the symmetrical adhesion of two cylindrical colloids to a tubular membrane. The adhesion of the rigid cylinders with different radius from the membrane tube surface can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. These significant structural behaviors can be obtained by analyzing the system energy. A second order adhesion transition from the desorbed to weakly adhered states is found, and a first order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered states can be obtained as well.     

Accurate double many-body expansion potential energy surface of HS_2(A~2A') by scaling the external correlation

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS_2 by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set. By using the double many-body expansion-scaled external correlation method,such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal · mol~(-1).The topographical features of the HS_2(A_2A') global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS_2(A_2A') can be used as a building block for constructing the global potential energy surfaces of larger S/H molecular systems and recommended for dynamic studies on the title molecular system.     

传能反应O(1D)+CO2(1Σ+g)→O(3P)+CO2(1Σ+g)中间物机理的理论研究

利用ab initio 量子化学方法研究了自旋禁阻的传能反应O(1D)+CO2(1Σ+g)→O(3P)+CO2(1Σ+g)的反应机制, 通过中间化合物CO3的单、三重态的势能面交叉点的确认, 证明了中间物传能机理的可行性. 同时计算了交叉点处的自旋-轨道偶合和面间跃迁几率, 进一步证明了中间化合物CO3的形成在传能过程中的重要作用.     

Exact quantum dynamics study of the H(2S)+SiH+(X1Σ+) reaction on a new potential energy surface of SiH2+(X2A1)

Based on a new global potential energy surface of SiH₂⁺(X²A₁), the exact quantum dynamical calculation for the H(²S)+SiH⁺(X¹Σ⁺)→H₂+Si⁺ reaction has been carried out by using the Chebyshev wave packet method. The initial state specified (ν_i=0, j_i=0) probabilities, integral cross sections (ICS) and thermal rate constants of the title reaction are calculated. All partial wave contributions up to J=90 are calculated in exact quantum calculation including the full Coriolis coupling (CC) effect. The dynamical behaviors of probabilities, ICSs and rate constants are found to be in accord with an exothermic reaction without potential barrier. By comparing the probabilities of CC with the corresponding centrifugal sudden (CS) approximation ones, it can be concluded that neglecting CC effect will decrease the collision time, increase the amplitude of oscillation and lead to overestimation or underestimation of the reaction probability. For ICSs and rate constants, it is found that the deviation of CC and CS ICSs is small in the most of collision energy range except for the range of 0 eV-0.05 eV, while the deviation of both rate constants is considerable in the temperature range of 16 K-1000 K.     

Time-dependent theoretical approach to the influence of laser fields on the resonance enhanced multi-photon ionization of SH radical

This paper reports that the (2+1) resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic states, i.e.~a¹Δ and b¹∑⁺, are involved in the simulation. It gives the simulated photoelectron spectra, the population in each electronic state, as well as the projection of the wave-packet in each electronic state on different vibrational states. These results show that the so-called four-state model can represent the experimental results well.     

Quantum and quasiclassical dynamics of C($^{3} P$) + H$_{2}(^{1} \varSigma_{\text{g}}^+)\rightarrow H(^{2} S)$ + CH($^{2} \varPi$) reaction: Coriolis coupling effects and stereodynamics

The dynamics of ${\rm C}+{\rm H_2}\rightarrow {\rm H}+{\rm CH}$ reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods. The analysis of reaction probabilities, integral cross sections, and rate coefficients reveal the essential Coriolis coupling effects in the quantum mechanical wave packet calculations.The calculated polarization-dependent differential cross section, $P$($\theta_r$) and $P$($\phi_r$) show that the $\bm j'$ of product rotational angular momentum is not only aligned along the $y$ axis and the direction of the vector $\bm x+\bm z$, but also strongly oriented along the positive $y$ axis.