P. L. Chapovsky
Molecular center-of-mass motion is taken into account in the theory of coherent control of nuclear spin isomers of molecules. It is shown that infrared radiation resonant to the molecular rovibrational transition can substantially enrich nuclear spin isomers and speed up their conversion rate.
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We report on a new phenomenon of molecular nuclear spin isomers conversion in the field of resonant laser radiation. It is based on the isomer-selective optical excitation and the difference of conversion rates for excited and unexcited molecules. We expect the considerable magnitude of the effect for all molecules which absorb the radiation of existing lasers.
The gas-phase structures of four difluoroiodobenzene and two dihydroxybromobenzene isomers were identified by correlating the emission angles of atomic fragment ions created following femtosecond laser-induced Coulomb explosion. The structural determinations were facilitated by confining the most polarizable axis of each molecule to the detection plane prior to the Coulomb explosion event using one-dimensional laser-induced adiabatic alignment. For a molecular target consisting of two difluoroiodobenzene isomers, each constituent structure could additionally be singled out and distinguished.
Glycans play a central role as mediators in most biological processes, but their structures are complicated by isomerism. Epimers and anomers, regioisomers, and branched sequences contribute to a structural variability that dwarfs those of nucleic acids and proteins, challenging even the most sophisticated analytical tools, such as NMR and mass spectrometry. Here, we introduce an electron tunneling technique that is label-free and can identify carbohydrates at the single-molecule level, offering significant benefits over existing technology. It is capable of analyzing sub-picomole quantities o…
Enrichment of nuclear spin isomers of molecules by infrared radiation resonant to molecular rovibrational transition is considered. Special attention is given to the enrichment by light-induced crossing of far separated ortho and para states.
Isomer- and state-dependent ion-molecule reactions between Coulomb-crystallised Ca$^+$ ions and 1,2-dichloroethene
研究揭示了Ca$^+$离子与1,2-二氯乙烯异构体的异构体和态依赖反应，发现cis异构体比trans异构体更活跃，且基态反应活性较低，源于长寿命反应复合物的形成。
The astronomical observation of isopropyl cyanide further stresses the link between the chemical composition of the ISM and molecular composition of the meteorites in which there is a dominance of branched chain amino acids as compared to the straight. However, observations of more branched chain molecules in ISM will firmly establish this link. In the light of this, we have considered C5H9N isomeric group in which the next higher member of the alkyl cyanide and other branched chain isomers belong. High-level quantum chemical calculations have been employed in estimating accurate energies of t…
Nuclear Spin Isomers and the Pauli Principle in Polaritonic Chemistry
研究核自旋异构体与泡利原理在极子化学中的影响，通过数值模拟和分析模型展示集体光-物质耦合的重塑作用。
An increasing number of large molecules have been positively identified in space. Many of these molecules are of biological interest and thus provide insight into prebiotic organic chemistry in the protoplanetary nebula. Among these molecules, acetic acid is of particular importance due to its structural proximity to glycine, the simplest amino acid. We compute electronic and vibrational properties of acetic acid and its isomers, methyl formate and glycolaldehyde, using density functional theory. From computed photo-absorption cross-sections, we obtain the corresponding photo-absorption rates …
A theoretical model of nuclear spin conversion in molecules controlled by an external electromagnetic radiation resonant to rotational transition has been developed. It has been shown that one can produce an enrichment of spin isomers and influence their conversion rates in two ways, through coherences and through level population change induced by radiation. Influence of conversion is ranged from significant speed up to almost complete inhibition of the process by proper choice of frequency and intensity of the external field.
An explorative quantum chemical study of the triatomic molecule IYPt, its isomers, group 17 congeners, and dimer is carried out. The results indicate that IYPt is a ground-state singlet with a bent geometry and a large electric dipole moment of magnitude 4.8 D. The IPtY isomer also is bent but 33.5 kcal/mol higher in energy whereas the isomer with the central iodine atom is not stable a molecule. Furthermore, the calculations indicate that only the dimer of IYPt, made of a (PtY)2 rhombus with the iodine atoms bonded to Y, is characterized by positive vibrational frequencies.
We have selected and spatially separated the two conformers of 3-aminophenol (C$_6$H$_7$NO) present in a molecular beam. Analogous to the separation of ions based on their mass-to-charge ratios in a quadrupole mass filter, the neutral conformers are separated based on their different mass-to-dipole-moment ratios in an ac electric quadrupole selector. For a given ac frequency, the individual conformers experience different focusing forces, resulting in different transmissions through the selector. These experiments demonstrate that conformer-selected samples of large molecules can be prepared, …
Theoretical model of the coherent control of nuclear spin isomers by microwave radiation has been developed. Model accounts the M-degeneracy of molecular states and molecular center-of-mass motion. The model has been applied to the 13CH3F molecules. Microwave radiation excites the para state (J=11,K=1) which is mixed by the nuclear spin-spin interaction with the ortho state (9,3). Dependencies of the isomer enrichment and conversion rates on the radiation frequency have been calculated. Both spectra consist of two resonances situated at the centers of allowed and forbidden (by nuclear spin) tr…
Using the Gaussian-03 for ab initio calculations, interactions of various acid molecules with a single water molecule were studied. The molecular and supermolecular optimized structures were found with the Becke-3-Lee-Yang-Parr (B3LYP-hybrid potential) calculations of density- functional theory (DFT) methods, as well as the Møller-Plesset second-order perturbation theory using the basis set of aug-cc-pVDZ quality and the CRENBL ECP effective core potential for molecules containing heavy iodine atom. Possible isomers of studied acids and supermolecules consisting of acid molecules coupled with …
We consider laser alignment of ortho and para spin isomers of water molecules by using strong and short off-resonance laser pulses. A single pulse is found to create a distinct transient alignment and antialignment of the isomeric species. We suggest selective alignment of one isomeric species (leaving the other species randomly aligned) by a pair of two laser pulses.
Controlling selectivity of reactions is a quest in chemistry. Here, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope. Characterization of voltage dependence of the reactions and determination of reaction rates demonstrate selectivity in constitutional isomerization reactions and provide insight i…
Using the Gaussian-03 for ab initio calculations, we have studied interaction of different acid molecules with a single water molecule. The molecular and supermolecular optimized structures were found with the Becke-3-Lee-Yang-Parr (B3LYP-hybrid potential) calculations of density-functional theory (DFT) methods as well as the Moeller-Plesset second-order perturbation theory, using the basis set of Aug-cc-pVDZ quality and the CRENBL ECP effective core potential for molecules containing heavy iodine atom. Possible isomers of studied acids and supermolecules, consisting of acid molecules coupled …
Accurate enthalpies of formation are reported for known and potential astromolecules using high level ab initio quantum chemical calculations. A total of 130 molecules comprising of 31 isomeric groups and 24 cyanide/isocyanide pairs with atoms ranging from 3 to 12 have been considered. The results show an interesting, surprisingly not well explored, relationship between energy, stability and abundance (ESA) existing among these molecules. Among the isomeric species, isomers with lower enthalpies of formation are more easily observed in the interstellar medium compared to their counterparts wit…
Using the concept of the so-called quantum relaxation, we build a semiphenomenological model for orto-para conversion of nuclear spin isomers of hydrogen-type molecules.
Water, H$_2$O, is one of the fundamental molecules in chemistry, biology and astrophysics. It exists as two distinct nuclear-spin isomers, para- and ortho-water, which do not interconvert in isolated molecules. The experimental challenges in preparing pure samples of the two isomers have thus far precluded a characterization of their individual chemical behaviour. Capitalizing on recent advances in the electrostatic deflection of polar molecules, we separated the ground states of para- and ortho-water in a molecular beam to show that the two isomers exhibit different reactivities in a prototyp…
Probing the structure of cyclic hydrocarbon molecules with X-ray-induced Coulomb explosion imaging
本研究利用X射线诱导库仑爆炸成像技术，区分了三种C7H8碳氢化合物异构体，展示了无需特定标记原子即可解析分子结构的方法。
Large molecules have complex potential-energy surfaces with many local minima. They exhibit multiple stereo-isomers, even at very low temperatures. In this paper we discuss the different approaches for the manipulation of the motion of large and complex molecules, like amino acids or peptides, and the prospects of state- and conformer-selected, focused, and slow beams of such molecules for studying their molecular properties and for fundamental physics studies. Accepted for publication in Faraday Disc. 142 (2009), DOI: 10.1039/b820045a
To unravel the structures of C12H12O7 isomers, identified as light-absorbing photooxidation products of syringol in atmospheric chamber experiments, we apply a graph-based molecule generator and machine learning workflow. To accomplish this in a bias-free manner, molecular graphs of the entire chemical subspace of C12H12O7 were generated, assuming that the isomers contain two C6-rings; this led to 260 million molecular graphs and 120 million stable structures. Using quantum chemistry excitation energies and oscillator strengths as training data, we predicted these quantities using kernel ridge…
In strong laser fields, sub-femtosecond control of chemical reactions with the carrier-envelope phase (CEP) becomes feasible. We have studied the control of reaction dynamics of acetylene and allene in intense few-cycle laser pulses at 750 nm, where ionic fragments are recorded with a reaction microscope. We find that by varying the CEP and intensity of the laser pulses it is possible to steer the motion of protons in the molecular dications, enabling control over deprotonation and isomerization reactions. The experimental results are compared to predictions from a quantum dynamical model, whe…
It is predicted that nuclear spin conversion in molecules can be efficiently controlled by strong laser radiation resonant to rovibrational molecular transition. The phenomenon can be used for substantial enrichment of spin isomers, or for detection of very weak (10-100 Hz) interactions in molecules.
Almost 20% of the ~ 200 different species detected in the interstellar and circumstellar media present a carbon atom linked to nitrogen by a triple bond. Among these 37 molecules, 30 are nitrile R-CN compounds, the remaining seven belonging to the isonitrile R-NC family. How these species behave in presence of the grain surfaces is still an open question. In this contribution we investigate whether the difference between nitrile and isonitrile functional groups may induce differences in the adsorption energies of the related isomers at the surfaces of interstellar grains of different nature an…
Spin degrees of freedom of water molecule in gas and liquid state were investigated in order to provide a reasonable answer about the unsolved problem of a long-term behavior of water spin isomers. The approach used involves an assumption that molecules change their spin state from a pure state to a mixed one when they interact with some sorts of adsorbent surface. Some models and conceptions of the quantum information processing were used.
A sequential acid-base (SAB) mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds
本文提出顺序酸碱（SAB）机制，通过HCOOH与HCO+和NH3的循环破坏与再形成过程解释暗分子云中顺式甲酸的出现，并计算其相对反式甲酸的比例为25.7%。
We present a novel method for the simulation of the vibration-induced autoionization dynamics in molecular anions in the framework of the quantum-classical surface hopping approach. Classical trajectories starting from quantum initial conditions are propagated on a quantum-mechanical potential energy surface while allowing for autoionization through transitions into discretized continuum states. These transitions are induced by the couplings between the electronic states of the bound anionic system and the electron-detached system composed of the neutral molecule and the free electron. A discr…
Water exists as two nuclear-spin isomers, para and ortho, determined by the overall spin of its two hydrogen nuclei. For isolated water molecules the conversion between these isomers is forbidden and they act as different molecular species. Yet, these species are not readily separable, and little is known about their specific physical and chemical properties, conversion mechanisms, or interactions. Here we demonstrate the production of isolated samples of both spin isomers in pure beams of para and ortho water, with both species in their respective absolute ground state. These single-quantum-s…
Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur containing candidate molecul…
Quantum theory of molecular orientation
本文提出了一种分子取向的量子理论，通过构建量子相空间，探讨了刚性分子的旋转和核自旋状态，并揭示了周期性旋转对称态空间中旋转-自旋纠缠和纤维自由度的特性，为量子纠错和容错量子门提供了新思路。
Para- and ortho- isomers of water have different chemical and physical properties. Excitations by magnetic field, laser emission or hydrodynamic cavitation are reported to change energetic levels and spin configurations of water molecules that in turn change macroscopically measurable properties of aqueous solutions. Similar scheme is also explored for dissolved molecular oxygen, where physical excitations form singlet oxygen with different spin configurations and generate a long chain of ionic and free-radical reactions. This work utilizes electrochemical impedance spectroscopy (EIS) to chara…
When the interaction between a molecular system and confined light modes in an optical or plasmonic cavity is strong enough to overcome the dissipative process, hybrid light-matter states (polaritons) become the fundamental excitations in the system. The mixing between the light and matter characters modifies the photophysical and photochemical properties. Especially, it was reported that these polaritons can be employed to control photochemical reactions, charge and energy transfer, and other processes. In addition, according to recent studies, vibrational strong coupling can be employed to r…
Molecular switches on metal surfaces typically show very little photoreactivity. Using scanning tunneling microscopy we show that the ring-opening/-closing switch nitrospiropyran thermally and optically isomerizes to the open merocyanine form on a Bi(110) surface. Irradiation by blue light of a monolayer spiropyran molecules leads to mixed domains of the two isomers. At large illumination intensities a photostationary state is established, indicating the bidirectional ring-opening and closing reaction of these molecules on the bismuth surface. The enhanced photoactivity contrasts with the case…
Photoswitchable molecules display two or more isomeric forms that may be accessed using light. Separating the electronic absorption bands of these isomers is key to selectively addressing a specific isomer and achieving high photostationary states whilst overall red-shifting the absorption bands serves to limit material damage due to UV-exposure and increases penetration depth in photopharmacological applications. Engineering these properties into a system through synthetic design however, remains a challenge. Here, we present a data-driven discovery pipeline for molecular photoswitches underp…
The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry-Pérot Fourier-transform microwave spectroscopy between 6 and 40~GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35-37~kcal/mol less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determ…
Molecular structure is often considered as emerging from the decoherence effect of the environment. Electrons are part of the environment of the nuclei in a molecule. In this work, their contribution to the classical-like geometrical relationships often observed between nuclei in molecular systems is investigated. Reduced density matrix (RDM) elements are evaluated from electron-nucleus wave functions. The computational results show that the electrons play a role in the localization of the nuclei around specific geometries. Although the electronic environment alone cannot explain molecular sym…
Density functional theory (DFT) calculations have been performed for the high-spin (HS) and low-spin (LS) isomers of a series of iron(II) spin crossover complexes with nitrogen ligands. The calculated charge densities have been analyzed in the framework of the quantum theory of atoms in molecules (QTAIM). For a number of iron(II) complexes with substituted tris(pyrazolyl) ligands the energy difference between HS and LS isomers, the spin state splitting, has been decomposed into atomic contributions in order to rationalize changes of the spin state splitting due to substituent effects.
Quantum mechanical dataset of 836k neutral closed shell molecules with upto 5 heavy atoms from CNOFSiPSClBr
该研究构建了覆盖最多5个重原子的836k中性闭壳层分子数据集VQM24，包含DFT和DMC能量及多种性质，并揭示其原子化能机器学习任务比QM9更难，为量子ML模型提供高保真基准。
The chemical composition of Titan organic haze is poorly known. To address this issue, laboratory analogs named tholins are synthesized, and analyzed by methods requiring often an extraction process in a carrier solvent. These methods exclude the analysis of the insoluble tholins fraction and assume a hypothetical chemical equivalence between soluble and insoluble fractions. In this work, we present a powerful complementary analysis method recently developed on the DESIRS VUV synchrotron beamline at SOLEIL. It involves a soft pyrolysis of tholins at ~230 deg C and an electron ion coincidence a…
We consider solid surface scattering of molecules that were subject to strong non-resonant ultrashort laser pulses just before hitting the surface. The pulses modify the rotational states of the molecules, causing their field free alignment, or a rotation with a preferred sense. We show that field-free laser-induced molecular alignment leads to correlations between the scattering angle and the sense of rotation of the scattered molecules. Moreover, by controlling the sense of laser induced unidirectional molecular rotation, one may affect the scattering angle of the molecules. This provides a …
Discovery of atomistic systems with desirable properties is a major challenge in chemistry and material science. Here we introduce a novel, autoregressive, convolutional deep neural network architecture that generates molecular equilibrium structures by sequentially placing atoms in three-dimensional space. The model estimates the joint probability over molecular configurations with tractable conditional probabilities which only depend on distances between atoms and their nuclear charges. It combines concepts from state-of-the-art atomistic neural networks with auto-regressive generative model…
In this review paper we introduce at first the cage nature of diamondoid molecules, the variety of their crystalline lattice structures, the nature of their structural isomers, their stereoisomers, and their other molecular specificities. The natural occurrence of diamondoids in petroleum fluids and how they come to be present in such fluids is introduced. Field experiences of phase transitions and depositions as well as techniques for separation, detection and measurement of diamondoids from petroleum fluids is presented and discussed. It is demonstrated that due to their six or more linking …
In recent years it became possible to align molecules in free space using ultrashort laser pulses. Here we explore two schemes for controlling molecule-surface scattering process, which are based on the laser-induced molecular alignment. In the first scheme, a single ultrashort non-resonant laser pulse is applied to a molecular beam hitting the surface. This pulse modifies the angular distribution of the incident molecules, and causes the scattered molecules to rotate with a preferred sense of rotation (clockwise or counter-clockwise). In the second scheme, two properly delayed laser pulses ar…
The understanding of molecular structure and function is at the very heart of the chemical and molecular sciences. Experiments that allow for the creation of structurally pure samples and the investigation of their molecular dynamics and chemical function have developed tremendously over the last few decades, although "there's plenty of room at the bottom" for better control as well as further applications. Here, we describe the use of inhomogeneous electric fields for the manipulation of neutral molecules in the gas-phase, \ie, for the separation of complex molecules according to size, struct…
A better understanding of sulphur chemistry is needed to solve the interstellar sulphur depletion problem. A way to achieve this goal is to study new S-bearing molecules in the laboratory, obtaining accurate rest frequencies for an astronomical search. We focus on dithioformic acid, HCSSH, which is the sulphur analogue of formic acid. The aim of this study is to provide an accurate line list of the two HCSSH $trans$ and $cis$ isomers in their electronic ground state and a comprehensive centrifugal distortion analysis with an extension of measurements in the millimetre and submillimetre range. …
A gas-phase formation route is proposed for the recently detected propargylimine molecule. In analogy to other imines, such as cyanomethanimine, the addition of a reactive radical (C$_2$H in the present case) to methanimine (CH$_2$NH}) leads to reaction channels open also in the harsh conditions of the interstellar medium. Three possible isomers can be formed in the C$H_2$NH + C$_2$H reaction: Z- and E-propargylimine (Z-,E-PGIM) as well as N-ethynyl-methanimine (N-EMIM). For both PGIM species, the computed global rate coefficient is nearly constant in the 20-300 K temperature range, and of the…
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