A strong inhomogeneous static electric field is used to spatially disperse a supersonic beam of polar molecules, according to their quantum state. We show that the molecules residing in the lowest-lying rotational states can be selected and used as targets for further experiments. As an illustration, we demonstrate an unprecedented degree of laser-induced 1D alignment $(<\cos^2θ_{2D}>=0.97)$ and strong orientation of state-selected iodobenzene molecules. This method should enable experiments on pure samples of polar molecules in their rotational ground state, offering new opportunities in molecular science.
We theoretically consider the phenomenon of field-free long-lasting orientation of symmetric-top molecules ionized by two-color laser pulses. The anisotropic ionization produces a significant long-lasting orientation of the surviving neutral molecules. The degree of orientation increases with both the pulse intensity and, counterintuitively, with the rotational temperature. The orientation may be enhanced even further by using multiple delayed two-color pulses. The long-lasting orientation may be probed by even harmonic generation or by Coulomb-explosion-based methods. The effect may enable th…
Making the best of mixed-field orientation of polar molecules: A recipe for achieving adiabatic dynamics in an electrostatic field combined with laser pulses
Chirality and chiral molecules are key elements in modern chemical and biochemical industries. Individual addressing, and the eventual separation of chiral enantiomers has been and still is an important elusive task in molecular physics and chemistry, and a variety of methods has been introduced over the years to achieve this goal. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces an enantioselective orientation of these molecules. This orientation persists for a long time, exceeding the…
We present a comprehensive study of enantioselective orientation of chiral molecules excited by a pair of delayed cross-polarized femtosecond laser pulses. We show that by optimizing the pulses' parameters, a significant (~ 10%) degree of enantioselective orientation can be achieved at zero and at five kelvin rotational temperatures. This study suggests a set of reasonable experimental conditions for inducing and measuring strong enantioselective orientation. The strong enantioselective orientation and the wide availability of the femtosecond laser systems required for the proposed experiments…
Both the translational diffusion coefficient $D$ and the electrophoretic mobility $μ$ of a short rod-like molecule (such as dsDNA) that is being pulled towards a nanopore by an electric field should depend on its orientation. Since a charged rod-like molecule tends to orient in the presence of an inhomogeneous electric field, $D$ and $μ$ will change as the molecule approaches the nanopore, and this will impact the capture process. We present a simplified study of this problem using theoretical arguments and Langevin Dynamics simulations. In particular, we introduce a new \textit{orientational …
Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g. intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of deg…
We study the excitation of asymmetric-top (including chiral) molecules by two-color femtosecond laser pulses. In the cases of non-chiral asymmetric-top molecules excited by an orthogonally polarized two-color pulse, we demonstrate, classically and quantum mechanically, three-dimensional orientation. For chiral molecules, we show that the orientation induced by a cross-polarized two-color pulse is enantioselective along the laser propagation direction, namely, the two enantiomers are oriented in opposite directions. On the short time scale, the classical and quantum simulations give results tha…
Theoretical description of mixed-field orientation of asymmetric top molecules: a time-dependent study
通过求解含时薛定谔方程，对倾斜电场和非共振线偏振激光脉冲作用下非对称陀螺分子的混合场取向进行了理论研究.在此框架下，我们计算了苯腈（C $_7$ H $_5$ N）的选态分子束的混合场取向，并与实验结果进行了比较[J. L. Hansen等人，A 83，023406（2011）]，并且利用我们先前的时间无关描述[J.J.Omiste等人，13，18815（2011）]。对于一个激发转动态，我们研究了混合场实验中使用的几种场配置的场修饰动力学。详细分析了非绝热现象及其对转动动力学的影响。
An ideal nanofabrication method should allow the organization of nanoparticles and molecules with nanometric positional precision, stoichiometric control and well-defined orientation. The DNA origami technique has evolved into a highly versatile bottom-up nanofabrication methodology that fulfils almost all of these features. It enables the nanometric positioning of molecules and nanoparticles with stoichiometric control, and even the orientation of asymmetrical nanoparticles along predefined directions. However, orienting individual molecules has been a standing challenge, mainly due to unspec…
We describe an apparatus to study the fragmentation of ion-molecule clusters triggered by laser excitation and transfer of an electron from the iodide to the neutral molecule. The apparatus comprises a source to generate ion-molecule clusters, a time-of-flight (TOF) spectrometer and a mass filter to select the desired anions, and a linear-plus-quadratic reflectron mass spectrometer to discriminate the fragment anions after the femtosecond laser excites the clusters. The fragment neutrals and anions are then captured by two channeltron detectors. The apparatus performance is tested by measuring…
Direct imaging of enantiomer-specific orientation dynamics in unidirectionally rotating chiral molecules
Institute of Science Tokyo（东京科学大学）；Kitasato University（北里大学）；The Weizmann Institute of Science（魏茨曼科学研究所）；Xiamen University（厦门大学）；The University of British Columbia（不列颠哥伦比亚大学）；Stewart Blusson Quantum Matter Institute（斯图尔特·布拉森量子物质研究所）
We investigate the translocation of rods with different charge distributions using hybrid Langevin Dynamics and Lattice Boltzmann (LD-LB) simulations. Electrostatic interactions are added to the system using the $P^3M$ algorithm to model the electrohydrodynamic interactions (EHI). We first examine the free-solution electrophoretic properties of rods with various charge distributions. Our translocation simulation results suggest that the order parameter is asymmetric during the capture and escape processes despite the symmetric electric field lines, while the impacts of the charge distribution …
The structure and quantum state of the reactants have a profound impact on the kinetics and dynamics of chemical reactions. Over the past years, significant advances have been made in the control and manipulation of molecules with external electric and magnetic fields in molecular-beam experiments for investigations of their state-, structure- and energy-specific chemical reactivity. Whereas studies for neutrals have so far mainly focused on weak-field-seeking species, we report here progress towards investigating reactions of strong-field-seeking molecules by introducing a novel crossed-molec…
Two-pulse field-free orientation reveals anisotropy of molecular shape resonance
我们报告的宏观无场取向的观察，即超过73%的CO分子指向同一方向。这是通过在高颗粒密度（$>10^{17}$ cm $^{-3}$）下操作的全光学方案来实现的，该方案组合了单色（$ω$）和双色（$ω+ 2ω$）非共振飞秒激光脉冲。我们表明，所实现的方向完全依赖于超极化相互作用，而不是电离耗尽机制，从而打开了广泛的应用。所实现的强取向使我们能够揭示由形状共振引起的光复合振幅和相位的分子框架各向异性。在28~eV附近的偶次谐波发射中出现共振的局部极大值。与此相反，奇次谐波发射被抑制在这个光谱区域中，通过一个不对称的光复合阶段和一个子周期斯塔克效应，通用的极性分子，我们实验确定的综合效果。
The laser-induced alignment-and-orientation (A&O) dynamics of the prolate symmetric top CH$_3$X (X = F, Cl, Br, I) molecules is investigated, with particular emphasis on the effect of halogen substitution on the rotational constants, dipole moments, and polarizabilities of these species, as these quantities determine the A&O dynamics. Insight into possible control schemes for preferred A&O dynamics of halogenated molecules and best practices for A&O simulations are provided, as well. It is shown that for accurate A&O-dynamics simulations it is necessary to employ large basis sets and high leve…
First principles based exploration of chemical space deepens our understanding of chemistry, and might help with the design of new materials or experiments. Due to the computational cost of quantum chemistry methods and the immens number of theoretically possible stable compounds comprehensive in-silico screening remains prohibitive. To overcome this challenge, we combine atoms-in-molecules based fragments, dubbed "amons" (A), with active learning in transferable quantum machine learning (ML) models. The efficiency, accuracy, scalability, and transferability of resulting AML models is demonstr…
Ultrashort laser pulses are widely used for transient field-free molecular orientation -- a phenomenon important in chemical reaction dynamics, ultrafast molecular imaging, high harmonics generation, and attosecond science. However, significant molecular orientation usually requires rotationally cold molecules, like in rarified molecular beams, because chaotic thermal motion is detrimental to the orientation process. Here we propose to use the mechanism of the echo phenomenon previously observed in hadron accelerators, free-electron lasers, and laser-excited molecules to overcome the destructi…
Enhancing Accuracy of Quantum-Selected Configuration Interaction Calculations using Multireference Perturbation Theory: Application to Aromatic Molecules
A new approach is presented to improve the performance of semiempirical quantum mechanical (SQM) methods in the description of noncovalent interactions. To show the strategy, the PM6 Hamiltonian was selected, although, in general, the procedure can be applied to other semiempirical Hamiltonians and to different methodologies. In this way, analytical corrections to PM6 were derived from fits to CCSD(T) - PM6 interaction energy differences. A set of small molecules was selected as representative of the common functional groups, and intermolecular potential energy curves were evaluated for the mo…
Correlation effects in strong-field ionization of heteronuclear diatomic molecules
我们发展了一个含时理论来研究强激光场作用下双原子分子的电子动力学和光电离过程，包括电子-电子关联效应。我们结合最近提出的含时广义活性空间组态相互作用理论[D。Hochstuhl和M. Bonitz，Phys.Rev.A86，053424（2012）; S. Bauch等人，Phys.Rev.A90，062508（2014）]，其具有包括局域轨道和连续态的长球形基组以描述束缚电子和传出光电子。作为例子，我们研究了双中心四电子氢化锂分子在不同强度区域的强场电离。利用单周期脉冲，研究了非对称异质结分子的两种取向：Li-H（电场从H指向Li）和H-Li（电场从H指向Li）。确定了电离的优选取向，并且我们发现从低强度的H-Li到高强度的Li-H的过渡。在不同的近似水平的电子相关性的影响进行了研究，我们发现一个显着的变化的优先取向。对于某些强度制度，甚至互换的首选配置观察，相对于不相关的模拟。进一步的洞察力提供了详细的光电子角分布的比较，并考虑到相关效应。
Enantioselective orientation of chiral molecules excited by a shaped picosecond laser pulse and a delayed femtosecond pulse is considered. Using quantum mechanical simulations, we demonstrate a strong field-free enantioselective orientation along the laser propagation direction. In addition, we use a classical model to reproduce the enantioselective orientation. Moreover, the analysis of the corresponding classical system allows understanding the qualitative features of the induced enantioselective orientation. The strong enantioselective orientation may be used for the separation of chiral en…
