Molecular Collisions Research Articles

Residual gas damping noise in constrained volume in space-borne gravitational wave detection

The residual gas damping in the enclosure surrounding a free-fall test mass is an important limiting factor for the sensitivity of some space detection missions. We present a constrained volume damping model for space-borne gravitational wave detection, which depends on the escape time needed for a molecule to diffuse out of the gap between two adjacent surfaces. Using a completely inelastic molecular collision prediction, we calculate the escape times in the two most common constrained volumes, cylinder and cuboid, respectively. Both calculations agree well with Monte Carlo simulations. Additionally, the theoretical model of the residual gas damping presented in this work is in good agreement with the experimental results in the ground torsion pendulum test of LISA and its precursor LISA Pathfinder.

Quantum state-resolved molecular dipolar collisions over four decades of energy.

Collisions between cold polar molecules represent a fascinating research frontier but have proven hard to probe experimentally. We report measurements of inelastic cross sections for collisions between nitric oxide (NO) and deuterated ammonia (ND3) molecules at energies between 0.1 and 580 centimeter-1, with full quantum state resolution. At energies below the ~100-centimeter-1 well depth of the interaction potential, we observed backward glories originating from peculiar U-turn trajectories. At energies below 0.2 centimeter-1, we observed a breakdown of the Langevin capture model, which we interpreted in terms of a suppressed mutual polarization during the collision, effectively switching off the molecular dipole moments. Scattering calculations based on an ab initio NO-ND3 potential energy surface revealed the crucial role of near-degenerate rotational levels with opposite parity in low-energy dipolar collisions.

Free-standing membrane incorporating single-atom catalysts for ultrafast electroreduction of low-concentration nitrate

The release of wastewaters containing relatively low levels of nitrate (NO3-) results in sufficient contamination to induce harmful algal blooms and to elevate drinking water NO3- concentrations to potentially hazardous levels. In particular, the facile triggering of algal blooms by ultra-low concentrations of NO3- necessitates the development of efficient methods for NO3- destruction. However, promising electrochemical methods suffer from weak mass transport under low reactant concentrations, resulting in long treatment times (on the order of hours) for complete NO3- destruction. In this study, we present flow-through electrofiltration via an electrified membrane incorporating nonprecious metal single-atom catalysts for NO3- reduction activity enhancement and selectivity modification, achieving near-complete removal of ultra-low concentration NO3- (10 mg-N L-1) with a residence time of only a few seconds (10 s). By anchoring Cu single atoms supported on N-doped carbon in a carbon nanotube interwoven framework, we fabricate a free-standing carbonaceous membrane featuring high conductivity, permeability, and flexibility. The membrane achieves over 97% NO3- removal with high N2 selectivity of 86% in a single-pass electrofiltration, which is a significant improvement over flow-by operation (30% NO3- removal with 7% N2 selectivity). This high NO3- reduction performance is attributed to the greater adsorption and transport of nitric oxide under high molecular collision frequency coupled with a balanced supply of atomic hydrogen through H2 dissociation during electrofiltration. Overall, our findings provide a paradigm of applying a flow-through electrified membrane incorporating single-atom catalysts to improve the rate and selectivity of NO3- reduction for efficient water purification.

The Meshless Direct Simulation Monte Carlo method

A new numerical simulation method called the Meshless Direct Simulation Monte Carlo (DSMC) Method is presented in this article for solving a rarefied flow field problem. It uses a discrete points group instead of using a conventional mesh to discretize the computational domain. The meshless theory is used to solve the governing equations of the rarefied flow field. Numerical challenges related to mesh distortion and low accuracy encountered in conventional mesh technology are eliminated. The meshless technology used in the DSMC method constructs the molecular cloud structure and the virtual volume to establish the methodology of molecular fast search, molecular collision pair number calculation, and molecular cloud sampling. The numerical results of a two-dimensional flow around a cylinder, a nozzle flow, a three-dimensional flow around a sphere, and a Mars probe re-entry flow are presented to demonstrate the feasibility, accuracy, and robustness of the Meshless DSMC method. This study provides the basis for meshless technology development in the field of rarefied flow.

Effects of synonymous mutations on kinetic properties and structure of firefly luciferase: Molecular dynamics simulation, molecular docking, RNA folding, and experimental study

Although synonymous mutations have long been thought to lack striking results, a growing body of research shows these mutations have highly variable effects. In this study, the impact of synonymous mutations in the development of thermostable luciferase was investigated using a combination of experimental and theoretical approaches. Using bioinformatics analysis, the codon usage features in the Lampyridae family's luciferases were studied and four synonymous mutations of Arg in luciferase were created. An exciting result was that the analysis of kinetic parameters showed a slight increase in the thermal stability of the mutant luciferase. AutoDock Vina, %MinMax algorithm, and UNAFold Server were used to perform molecular docking, folding rate, and RNA folding, respectively. Here, it was assumed that in the region (Arg337) with a moderate propensity for coil, synonymous mutation altered the rate of translation, which in turn may lead to a slight change in the structure of the enzyme. According to the molecular dynamics simulation data, local minor global flexibility is observed in the context of the protein conformation. A plausible explanation is that this flexibility may strengthen hydrophobic interactions due to its sensitivity to a molecular collision. Accordingly, thermostability originated mainly from hydrophobic interaction.

High-precision cavity-enhanced spectroscopy for studying the H2-Ar collisions and interactions.

Information about molecular collisions is encoded in the shapes of collision-perturbed molecular resonances. This connection between molecular interactions and line shapes is most clearly seen in simple systems, such as the molecular hydrogen perturbed by a noble gas atom. We study the H2-Ar system by means of highly accurate absorption spectroscopy and ab initio calculations. On the one hand, we use the cavity-ring-down-spectroscopy technique to record the shapes of the S(1) 3-0 line of molecular hydrogen perturbed by argon. On the other hand, we simulate the shapes of this line using ab initio quantum-scattering calculations performed on our accurate H2-Ar potential energy surface (PES). In order to validate the PES and the methodology of quantum-scattering calculations separately from the model of velocity-changing collisions, we measured the spectra in experimental conditions in which the influence of the latter is relatively minor. In these conditions, our theoretical collision-perturbed line shapes reproduce the raw experimental spectra at the percent level. However, the collisional shift, δ0, differs from the experimental value by 20%. Compared to other line-shape parameters, collisional shift displays much higher sensitivity to various technical aspects of the computational methodology. We identify the contributors to this large error and find the inaccuracies of the PES to be the dominant factor. With regard to the quantum scattering methodology, we demonstrate that treating the centrifugal distortion in a simple, approximate manner is sufficient to obtain the percent-level accuracy of collisional spectra.

Coherent Control of Ultracold Molecular Collisions: The Role of Resonances.

We consider the coherent control of ultracold molecule-molecule scattering, impacted by a dense set of rovibrational resonances. To characterize the resonance spectrum, a rudimentary model based on multichannel quantum defect theory has been used to study the control of the scattering cross section and the reaction rate. Complete control around resonance energies is shown to be possible, but thermal averaging over a large number of resonances significantly reduces the extent of control of reaction rates related to the random distribution of optimal control parameters between resonances. We show that measuring the extent of coherent control could be used to extract meaningful information about the relative contribution of direct scattering versus collision complex formation, as well as about the statistical regime.

NIR Photocontrolled Fluorescent Nanosensor under a Six-Branched DNA Nanowheel-Induced Nucleic Acid Confinement Effect for High-Performance Bioimaging.

Although DNA nanotechnology is a promising option for fluorescent biosensors to perform bioimaging, the uncontrollable target identification during biological delivery and the spatially free molecular collision of nucleic acids may cause unsatisfactory imaging precision and sensitivity, respectively. Aiming at solving these challenges, we herein integrate some productive notions. On the one hand, the target recognition component is inserted with a photocleavage bond and a core-shell structured upconversion nanoparticle with a low thermal effect is further employed to act as the ultraviolet light generation source, under which a precise near-infrared photocontrolled sensing is achieved through a simple external 808 nm light irradiation. On the other hand, the collision of all of the hairpin nucleic acid reactants is confined by a DNA linker to form a six-branched DNA nanowheel, after which their local reaction concentrations are vastly enhanced (∼27.48 times) to induce a special nucleic acid confinement effect to guarantee highly sensitive detection. By selecting a lung cancer-associated short noncoding microRNA sequence (miRNA-155) as a model low-abundance analyte, it is demonstrated that the newly established fluorescent nanosensor not only presents good in vitro assay performance but also exhibits a high-performance bioimaging competence in live biosystems including cells and mouse body, propelling the progress of DNA nanotechnology in the biosensing field.

Experimental and theoretical investigations of dispersion of ultrasonic waves in the low-temperature and low-pressure nitrogen gas.

Temperature has a complex effect on acoustic dispersion in dilute gases. In this paper, the effect of temperature on the acoustic dispersion of dilute gases is analyzed theoretically and experimentally. Theoretically, the Navier-Stokes (NS) equation and the Greenspan's theory, which includes the rotational-relaxation correction, are applied to calculate the dispersive sound speed. It is concluded that the temperature affects the molecular translational relaxation and the rotational relaxation by influencing the average molecular collision frequency and the relaxation collision number, respectively, and thus, change the amplitude of the acoustic dispersion. Numerical calculations led to the conclusion that both translational and rotational dispersions weakened as the temperature decreased. Experimentally, sound speed measurements of 21-40 kHz acoustic waves were also carried out in gaseous nitrogen at temperatures ranging from -70 °C to 20 °C and pressures of 150-105 Pa. Theoretical predications indicate that the speed of sound should increase with decreasing pressure at all temperatures, and the degree of dispersion should diminish at lower temperatures. The experimental observation of dispersion is consistent with theory within experimental error (1%) but was not able to distinguish the small (0.01%) increase in sound speed expected at 150 Pa.

Single- and double-ionization processes of antiproton-helium and antiproton–molecular hydrogen collisions in the keV energy range

We report on an ab initio model to describe single- and double-ionization processes in antiproton collisions with atoms and molecules. Our model is based on a fully correlated close-coupling approach and a Dyson orbital analysis. Furthermore, we employ the concept of a correlation integral in order to quantify and gain insights into the effects of electronic correlation on the ionization processes. Our model is applied to the prototype antiproton-helium and antiproton--molecular hydrogen collision systems in the keV energy range.

Ultracold Sticky Collisions: Theoretical and Experimental Status.

Collisional complexes, which are formed as intermediate states in molecular collisions, are typically short-lived and decay within picoseconds. However, in ultracold collisions involving bialkali molecules, complexes can live for milliseconds, completely changing the collision dynamics. This can lead to unexpected two-body loss in samples of nonreactive molecules. During the past decade, such "sticky" collisions have been a major hindrance in the preparation of dense and stable molecular samples, especially in the quantum-degenerate regime. Currently, the behavior of the complexes is not fully understood. For example, in some cases, their lifetime has been measured to be many orders of magnitude longer than recent models predict. This is not only an intriguing problem in itself but also practically relevant, since understanding molecular complexes may help to mitigate their detrimental effects. Here, we review the recent experimental and theoretical progress in this field. We treat the case of molecule-molecule as well as molecule-atom collisions.

MODELING of Rarefied Gas Flows Inside a Micro-Nozzle Based on the DSMC Method Coupled with a Modified Gas–Surface Interaction Model

In this study, we first considered the influence of micro-nozzle wall roughness structure on molecular collision and reflection behavior and established a modified CLL model. The DSMC method was used to simulate and analyze the flow of the micro-nozzle in the cold gas micro-propulsion system, and the deviation of simulation results before and after the improvement of CLL model were compared. Then, the rarefied flow characteristics under a small needle valve opening (less than 1%) were focused on the research, and the particle position, molecular number density, and spatial distribution of internal energy in the micro-nozzle were calculated. The spatial distributions of the flow mechanism in the micro-nozzle under different needle valve openings were compared and analyzed. It was found that when the needle valve opening is lower than 1%, the slip flow and transition flow regions move significantly upstream of the nozzle, the free molecular flow distribution region expands significantly, and the relationship between thrust force and needle valve opening is obviously different from that of medium and large needle valve openings. The effect of nitrogen temperature on the rarefied flow and thrust force is also discussed in this research. The numerical results showed that as gas temperature increases, the molecular internal energy, momentum, and molecular number density near the nozzle exit are enhanced. The thrust at small needle valve openings was significantly affected by the temperature of the working mass. The results of this study will provide key data for the design and development of cold gas micro-thrusters.

The Electronic Kinetics of Molecular Nitrogen and Molecular Oxygen in the Earth’s Middle Atmosphere during the GLE Events of Solar Cycle 23

Based on models of the electronic kinetics of triplet and singlet states of molecular nitrogen andsinglet states of molecular oxygen for the Earth’s middle atmosphere, we calculated the intensity profiles ofthe bands of the first and second positive N2 systems, the Lyman–Birge–Hopfield N2 bands, and the infraredO2 bands in the case of precipitation of high-energy protons during the GLE65, GLE67, GLE69, and GLE70events of solar cycle 23. Calculations have shown that almost over the entire interval of altitudes of 20–80 km,there is a significant contribution from the processes of quenching some electronically excited states of N2and O2 during molecular collisions. The kinetics of O2 singlet states at the altitudes of the middle atmosphereduring proton precipitation is considered taking into account both direct excitation by high-energy particlesand intermolecular processes of electron excitation transfer

THE STUDY OF KINETICS OF MOLECULAR NITROGEN IN THE STRATOSPHERE OF TITAN DURING PRECIPITATION OF GALACTIC COSMIC RAYS

We study the electronic kinetics of molecular nitrogen in the stratosphere of Titan during precipitation of galactic cosmic rays. The composition of Titan’s atmosphere at the altitudes is considered as the mixture of N2-CH4-H2-CO gases with admixtures of hydrocarbons. Special attention is paid to the investigation of the role of inelastic molecular collisions in the redistribution of the excitation energy between different molecular degrees of freedom. The inelastic intramolecular and intermolecular electron energy transfers during molecular collisions are taken into account in the calculation of vibrational populations of electronically excited states of N2 at the altitudes of the stratosphere. The important role of electronically excited molecular nitrogen in the production of CH3 radicals and H atoms is discussed.

Preparation of ultra-cold (36D<sub>5/2</sub>+ 6S<sub>1/2</sub>) Rydberg molecule and measurement of its permanent electric dipole moment

<sec>Ultra-cold long-range Rydberg molecules, consisting of a Rydberg atom and a ground-state atom or another Rydberg atom or ion, have attracted considerable attention due to their exaggerated properties, such as huge size, long chemical bond, large polarization and electric dipole moment, abundant vibrational states and exotic adiabatic potentials. The binding mechanism of Rydberg molecules is a low-energy scattering interaction between the Rydberg electron and the ground state atom for ground-Rydberg molecules or long-range multipole interaction for Rydberg-atom macrodimers and Rydberg-ion molecules, in contrast to covalent bonds, ionic bonds of normal and van der Waals interaction. Owing to its huge size, the dynamic evolution becomes slow compared with normal diatomic molecules and the ultra-long chemical bonds allow being imaged directly by high resolution imaging technology, which makes it convenient to observe the molecular dynamics process chemical reaction process in real time. The investigation of Rydberg molecules will be significant for understanding the mechanism of molecular collision and quantum chemical reaction.</sec><sec>In this work, we study the ultra-cold Rydberg-ground state molecules theoretically and experimentally. Theoretically, we calculate the adiabatic potential energy curve of cesium (36D<sub>5/2</sub>+ 6S<sub>1/2</sub>) Rydberg molecule based on the Fermi model of low energy electron scattering by numerically solving the Hamiltonian of Rydberg molecules. And also, we obtain its characteristic parameters, such as the potential depth, binding energy and equilibrium nuclear distance of Rydberg molecule. Experimentally, the Rydberg-ground molecules are investigated by a photoassociation spectroscopy, where two laser pulses are used to achieve a two-photon transition, and their spectra are obtained by ion detection technology. We successfully observe the Rydberg-ground state molecular spectra that correspond to a scattering triplet and a scattering single-triplet mixture (<sup>S,T</sup>Σ). The measured binding energy of Rydberg-ground state molecules is in good agreement with the theoretical result. In addition, taking the Rydberg-ground state molecules formed by scattering triplet (<sup>T</sup>Σ) for example, we demonstrate the spectrum broadening of Rydberg molecules in a weak electric field, from which we obtain the permanent electric dipole moments <inline-formula><tex-math id="M2">\begin{document}$|\bar{d}|$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M2.png"/></alternatives></inline-formula> of polar Rydberg-ground state molecules about (12.10<inline-formula><tex-math id="M3">\begin{document}$ \pm $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M3.png"/></alternatives></inline-formula>1.65) Debye ((4.76<inline-formula><tex-math id="M4">\begin{document}$ \pm $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221865_M4.png"/></alternatives></inline-formula>0.65) <i>ea</i><sub>0</sub>). The results are consistent with the theoretical calculations. Our study provides a feasible scheme for the experimental preparation of D-type Rydberg-ground molecules, which is of great significance in studying the binding mechanism and the spectral characteristics of polar Rydberg molecules.</sec>

Определение значений переносных характеристик в многокомпонентных средах на основе анализа микропроцессов

This paper proposes a two-level approach for mathematical modeling of processes in multicomponent gas mixtures. It involves a combination of the description of conservation laws based on macro-equations and the determination of the corresponding transfer coefficients using the analysis of micro-processes. The main purpose of this work is to develop an algorithm for determining transport characteristics in multicomponent media based on the analysis of inner micro-processes. Hence, the kinetic molecular theory of gases and liquids is used, namely, the collision part of the Boltzmann equation. It includes multiple improper integrals taking into account the effect of micro-processes in the medium on the values of transport coefficients. When integrating the Boltzmann equation by the Chapman-Enskog method, the transport coefficients are expressed through integral brackets of the Sonin polynomials, which represent the linear combinations of molecular collision integrals. Their calculations require the use of efficient mathematically sound ways including the elements of parallel computing.

A multi-degree-of-freedom gas kinetic multi-prediction implicit scheme

A multi-scale implicit multi-degree-of-freedom (MDOF) kinetic model with molecular translational, rotational and vibrational effects is presented. The evolution and exchange of energy among translational, rotational and vibrational degrees of freedom are demonstrated by three coupled relaxation processes. An orthogonal polynomial system is used to involve heat-transfer and viscosity properties in construction of a sequence of objective distribution functions at various relaxation stages. Based on finite volume discrete velocity method framework, the asymptotic preserving discrete unified gas-kinetic scheme (DUGKS) flux is adopted to preserve particle motion information. A second-order prediction scheme based on the Navier-Stokes flux is constructed to predict macroscopic variables from macroscopic residuals for implicit DUGKS iteration, which contains a multiple prediction methodology. The current MDOF kinetic model provides a concrete insight into energy exchange between the rotational and vibrational degrees of freedom during molecular inelastic collisions. The accurate prediction procedure significantly accelerates convergence. Several numerical test cases, including rarefied gas flow in lid-driven cavity, variable specific heat ratio shock structure, hypersonic circular cylinder flows at different Knudsen and Mach numbers, and hypersonic flat plate flow, are performed to validate the accuracy and efficiency of present model. All numerical results of the present method agreed well with those of the reference data. A 2∼3 orders-of-magnitude improvements in computational efficiency of the multi-scale implicit method are achieved compared with the explicit method. It demonstrated that the present method is a promising scheme considering vibration-rotation-translation energy exchange of poly-atomic molecules for the fast simulation of multi-scale flows from low-speed incompressible flow to hypersonic flow, from continuum to rarefied regime.

Landing Proteins on Graphene Trampoline Preserves Their Gas-Phase Folding on the Surface.

Molecule-surface collisions are known to initiate dynamics that lead to products inaccessible by thermal chemistry. These collision dynamics, however, have mostly been examined on bulk surfaces, leaving vast opportunities unexplored for molecular collisions on nanostructures, especially on those that exhibit mechanical properties radically different from those of their bulk counterparts. Probing energy-dependent dynamics on nanostructures, particularly for large molecules, has been challenging due to their fast time scales and high structural complexity. Here, by examining the dynamics of a protein impinging on a freestanding, single-atom-thick membrane, we discover molecule-on-trampoline dynamics that disperse the collision impact away from the incident protein within a few picoseconds. As a result, our experiments and ab initio calculations show that cytochrome c retains its gas-phase folded structure when it collides onto freestanding single-layer graphene at low energies (∼20 meV/atom). The molecule-on-trampoline dynamics, expected to be operative on many freestanding atomic membranes, enable reliable means to transfer gas-phase macromolecular structures onto freestanding surfaces for their single-molecule imaging, complementing many bioanalytical techniques.

SERS Monitored Kinetic Process of Gaseous Thiophenol Compound in Plasmonic MOF Nanoparticles.

Benefiting from the electromagnetic enhancement of noble metal nanoparticles (NPs) and the capture ability of organic frameworks, plasmonic metal-organic framework (MOF) structures have greatly promoted the development of gas detection by surface-enhanced Raman spectroscopy (SERS). In those detections, the kinetic process of gaseous molecules in plasmonic-MOF structures has a great influence on SERS spectra, which is still lacking intensive investigation in previous reports. In this work, the kinetic processes of gaseous thiophenol compounds (TPC) in the plasmonic Zeolitic Imidazolate Framework (Ag@ZIF) core-shell NPs are studied by SERS spectra. The experimental data demonstrate that the SERS intensities of gaseous TPC could be enhanced once more in an H2 mixed gas environment with different functional groups of TPC. Further results reveal that the two-step enhancement of SERS intensities is not only related to the thicknesses of the MOF shell but also affected by the ambient mixed gas. To understand this novel phenomenon, the binding energy between the gaseous molecule and ZIF is calculated based on first-principles computation. In combination with the plasmonic properties of the Ag core, a molecular collision model is introduced here to show the distribution of gaseous TPC molecules in ZIF, which could be responsible for this interesting two-step enhancement of SERS intensities. Furthermore, the H2 assisted kinetic process of gaseous p-aminothiophenol (PATP) is also analyzed by the classical pseudo-first-order kinetic model, which is consistent with our experimental SERS data. Our work not only reveals the novel phenomenon of plasmonic-MOF structures to improve the gas detection by SERS spectra but also enriches the understanding of the microcosmic process of gaseous molecules in the mixed gas environment to optimize MOF structures for gas capture and storage.

Hough Mode Extensions (HMEs) and Solar Tide Behavior in the Dissipative Thermosphere

AbstractThis paper quantifies and interprets how thermosphere dissipation in the form of molecular viscosity, molecular thermal conductivity and collisions with ions (“ion drag”) determines the height versus latitude structures of a variety of migrating and non‐migrating solar thermal tides, pole‐to‐pole up to 400 km altitude. This is done through computation of thermosphere Hough Mode Extensions (HMEs); that is, solutions to the linearized momentum, thermal energy, continuity, state and hydrostatic balance equations wherein the horizontal structure of troposphere forcing for each HME corresponds to the eigenfunction (Hough function) of Laplace's tidal equation for a particular tidal mode, and the background state and thermosphere dissipation are specified for nominal solar minimum, average and maximum activity conditions. The broad features revealed, different for each HME, include changes in vertical(horizontal) structure with latitude(height), degree of vertical penetration to the middle and upper thermosphere, changes in vertical wavelength (λz) with height due to the transition in background thermal gradient around the mesopause, and insights into role of ion drag in determining tidal amplitudes and their solar cycle variability. The HMEs are particularly useful for fitting measurements of tides, and for estimating tidal fields beyond those dependent variables actually fit and including those outside the fitting domain. The HMEs reported here were created as part of the Ionospheric CONnection (ICON) mission to serve as observation‐based lower boundary conditions for Thermosphere Ionosphere Mesosphere General Circulation Model‐ICON. Access to the full set of HMEs in tabular and graphical form is provided.