Yong-Chang Han

Given the relatively long wavelength of terahertz (THz) laser pulses, they are rarely applied to molecular vibrational excitation or photodissociation. To address this gap, we present the first report of molecular dissociation induced by a single THz pulse with the time-dependent wavepacket method. By using the pulse of 9 THz and 10 optical cycles, 40$\%$ dissociation probability of the ground LiBe molecule has been achieved. By analyzing the time-resolved rovibrational population distributions, it is demonstrated that the dissociation is primarily driven by the vibrational ladder-climbing mechanism. By optimizing the laser frequency and intensity, the maximum dissociation probability can be 76$\%$.

We study exotic orbits in the photoassociation process by considering both the vibrational and rotational motions in a classical model. In the presence of rotational motion, the exotic orbits possess regular bound segments even when the total energy exceeds the threshold energy of the interaction potential. Such features of the exotic orbits are interpreted by introducing an effective potential. We employ Lagrangian descriptors and escape time to characterize the phase-space structure and show that exotic orbits are distributed around the stable region in the short-range phase space. We further calculate the photoassociation probability. Our work provides new insights into the dynamical mechanisms of photoassociation processes.

Full-dimensional simulations reveal roaming as a general, nontraditional pathway. Its distinctive dynamics and energy redistribution significantly affect product branching and reaction rates, beyond the conventional minimum-energy-path paradigm.

范德瓦尔斯相互作用对原子与分子超冷碰撞有重要影响。本文研究了碱金属原子与碱金属极性双原子分子之间的范德瓦尔斯系数C₆。考虑分子处于¹Σ⁺电子态，基于微扰理论给出了转动基态分子与s/p/d态原子以及转动激发态分子与s态原子间的C₆表达式。以K-NaK体系为例，分析了C₆随振动量子数和转动量子数变化的趋势。通过对比对角化偶极-偶极相互作用矩阵得到的势能曲线和微扰得到的范德瓦尔斯势能曲线，确定了范德瓦尔斯势的适用范围。

Due to its potential applications in HF chemical lasers and its significance as a prototypical polyatomic reaction, the F + C₂H₆ reaction has long been a central topic in chemical kinetics and molecular dynamics. Although previous studies have reported both experimental and theoretical rate constants, discrepancies among these results persist. Moreover, the available experimental data do not cover the full temperature range, particularly at temperatures above room temperature, which are highly relevant to combustion and chemical laser applications. In this work, we report a new FI-NN potential energy surface (PES) developed at the gold-standard CCSD(T) level, which has been validated by its ability to reproduce HF rovibrational state distributions in close agreement with experimental results. Using this PES, we computed rate coefficients over the temperature range of 200-1100 K via direct ring-polymer molecular dynamics (RPMD). The calculated rates show good agreement with available experimental data in the low-temperature regime and extend reliable predictions to the high-temperature region relevant to combustion and chemical laser processes. These accurate RPMD rate coefficients can be combined with quasi-classical trajectory (QCT) calculations to yield reliable state-resolved dynamics and rate coefficients, thereby providing a consistent kinetic description across a broad temperature range.

Vacancies of Se and Sb are the most detrimental deep-level defects in the Sb2Se3 film. Herein, an approach is proposed to passivate the Sb vacancies using Al3+ ions. The tris(8-hydroxy-quinolinato) aluminum (Alq3) is employed as the Al3+ source, which is buried between indium tin oxide (ITO) and Sb2Se3. Additionally, the incorporation of the Alq3 layer not only inhibits the chemical reaction between Sb2Se3 and ITO but also lowers the contact barrier. As a result, the open-circuit voltage increases from 0.34 to 0.43 V, and the power conversion efficiency rises from 3.3% to 5.1%. Notably, our finding confirms that the grain boundary in the Sb2Se3 film with (020) preferred orientation is harmless and does not induce significant carrier recombination. The device is fabricated by conventional vacuum thermal evaporation. This study offers insights into enhancing the efficiency of Sb2Se3 solar cells.

The ladder-type population transfer of the HF molecule steered by four-color harmonic laser pulses (HLPs) is investigated using the time-dependent quantum wave packet method. It is found that although there exist large background excitations and many (resonant) transition pathways during the driving, nearly 100% of the population could be transferred to the target state. In particular, such a process could be coherently controlled by changing the phases of the four HLPs, especially the phases of the fundamental and second HLPs, which can be accounted for in large part by the combined effects of the corresponding transition pathways and the maximal amplitude of the total electric field. However, for manipulating the phases of the third and fourth HLPs, both the changes in the maximal electric field amplitude and the asymmetry size fail to guide the variation of the target-state population because of the correlated effects of all these transition pathways, particularly the ones that do not contain the third and fourth HLP excitations. Importantly, our results also denote that the variation of the maximal electric field amplitude may give a well qualitative prediction about the phase-controlled population when the manipulated phase is directly related to all the transition pathways, which is the general case in the widely used two-color scheme. In addition, the maximal amplitude of the total electric field tends to play a more important role than its asymmetry size in the phase-controlled population transfer process.