Rotational Excitation Research Articles

Real-time hydrogen molecular dynamics satisfying the nuclear spin statistics of a quantum rotor

Apparent presence of the nuclear-spin species of a hydrogen molecule, para-hydrogen and ortho-hydrogen, associated with the quantum rotation is a manifestation of the nuclear quantum nature of hydrogen, governing not only molecular structures but also physical and chemical properties of hydrogen molecules. It has been a great challenge to observe and calculate real-time dynamics of such molecularized fermions. Here, we developed the non-empirical quantum molecular dynamics method that enables real-time molecular dynamics simulations of hydrogen molecules satisfying the nuclear spin statistics of the quantum rotor. While reproducing the species-dependent quantum rotational energy, population ratio, specific heat, and H-H bond length and frequency, we found that their translational, orientational and vibrational dynamics becomes accelerated with the higher rotational excitation, concluding that the nuclear quantum rotation stemmed from the nuclear spin statistics can induce various kinds of dynamics and reactions intrinsic to each hydrogen species.

Diagnostics of a nanosecond atmospheric plasma jet. Electron and ro-vibrational excitation dynamics

Atmospheric repetitive He discharge with 10 ns current peak width and V s−1 voltage front rise working in jet geometry is studied. The first part of the study is devoted to electrical and optical discharge characterization including voltage-current behavior, emission dynamics, as well as ro-vibrational dynamics of N2, N and OH molecules. It is found that He atoms get excited at the very early stage, as a result of ionization wave formation. This process follows by excitation of O, N2 and N. It is also shown that a rather small (0.1%–1%) air admixtures facilitate gas breakdown, as revealed by shortening of the discharge current risetime. The rotational excitation of N always overtakes He excitation by about 5 ns, with rotational temperature peaking at about 650 K and decaying afterwards, whereas rotational temperature of N2 always remains constant equal to about 300 K. This value is associated with gas kinetic temperature since the electron-rotational (e-R) excitation process is too slow, so it cannot be activated during the plasma phase and no additional change in rotational excitation of N2 happens. Nitrogen molecules remain vibrationally excited in the discharge, post-discharge and jet areas after the plasma pulse which is likely a result of ionization wave propagation. Upon water vapor injection the apparent OH rotational distributions reveal double Boltzmann slope representing thermalized and non-thermalized OH groups. Rotational temperature of the thermalized group correlates with the one of N showing, however, much longer relaxation time, whereas for the non-thermalized group it remains above 1 eV at all conditions. The obtained results confirm that the studied ns- discharge is a good candidate for temperature-sensitive applications, such as the bio-sample treatment. Further analysis related to the ionization waves, electron density and electric field behavior is undertaken in the second part.

ESMGFZ Products for Earth Rotation Prediction

Abstract The Earth System Modelling Group of GeoForschungsZentrum Potsdam (ESMGFZ) provides geodetic products for gravity variations, Earth rotation excitations, and Earth surface deformations related to mass redistributions and mass loads in the atmosphere, ocean, and terrestrial water storage. Earth rotation excitation compiled as effective angular momentum (EAM) functions for each Earth subsystem (atmosphere, ocean, continental hydrology) are important for Earth rotation prediction. Especially the 6-day forecasts extending the model analysis runs offer essential information for the improvement of ultra-short-term Earth rotation predictions. In addition to the individual effective angular momentum function of each subsystem, ESMGFZ calculates a combined EAM prediction product. Adjusted to the official Earth orientation parameter (EOP) products IERS 14C04 and Bulletin A, this EAM prediction product allows to extrapolate the polar motion and Length-of-Day parameter time series for 90 days into the future via the Liouville equation. ESMGFZ submits such an EOP prediction to the 2nd EOPPCC campaign.

Investigation on plasma enhanced decomposition of ammonium dinitramide (ADN) based propellant with optical diagnosis

Plasma-enhanced decomposition is a promising method to achieve reliable ignition and better thruster performance with an ADN-based propellant. High-speed imaging and optical emission spectroscopy are used to characterize the discharge plasma produced from ADN-based propellant vapor and argon carrier gas within parallel planes. Discharge regimes are independently controlled by varying working parameters. The transition from abnormal glow discharge (AGD) to filamentary discharge (FD) is identified from voltage-current characteristics and sudden changes in excitation electron temperature (Te-exc) and electron density (Ne) under a pressure of 0.2–10 kPa. Instabilities develop because there are more freedom degrees and higher collision probabilities after ADN-based propellant vapor is added. The product of Te-exc and Ne shows a higher energy transfer efficiency from input power to vapor in the FD regime. Water molecules increase the net dissociative attachment rate and effectively quench Ne. Although preheated vapor (as the discharge medium) has a much lower Ne, more radicals appear such as OH, NH, CH, CN, N2, N2+, and C2, which promote chemical interactions in an electric field and increase the probability of successful ignition. This can be attributed to thermalization due to an increase in the translational kinetic energy and rotational excitation, which has an important impact on chemical reaction kinetics. Therefore, preheating is verified as critical for improving the ignition and performance of a plasma-assisted ADN-based thruster.

Analysis and experiment of auxetic centrifugal softening impact energy harvesting from ultra-low-frequency rotational excitations

The ubiquitous ultra-low-frequency rotational motions have become a kind of potential source for energy harvesting. Despite this, achieving high energy output at ultra-low rotational frequencies via simple energy harvesting structures appears to be a significant challenge. Therefore, this paper proposes an auxetic centrifugal softening impact energy harvester (ASIEH) to break through this bottleneck. The ASIEH consists of a centrifugal softening driving beam that impacts two rigid auxetic piezoelectric beams to generate electric energy during rotation. The modeling and simulation of the ASIEH and the plain centrifugal softening impact energy harvester (PSIEH) indicate that the high stress distribution and the simultaneous operation of d31 and d32 modes of the auxetic energy harvester can improve the energy output. Under the centrifugal effect, the driving beam experiences the vibration, impact and trapping modes subsequently, among which the impact mode produces the highest energy output. Experiments are conducted to validate the model and show that the peak power of the ASIEH (0.673 mW) can be increased by 200.45% compared with that of the PSIEH (0.224 mW) at 3.5 Hz. Parametric studies indicate that no matter how the impact distance and rotational radius are varied, the peak power and bandwidth of the ASIEH are higher than those of the PSIEH. Owing to the combination of both the centrifugal effect and the auxetic structure, the proposed ASIEH exhibits the great potential in ultra-low-frequency rotational energy harvesting with both high power density (41.23 μW/g) and high output power.

Molecular orientation echoes via concerted terahertz and near-IR excitations.

A new and efficient method for orientation echo spectroscopy is presented and realized experimentally. The excitation scheme utilizes concerted rotational excitations by both ultrashort terahertz and near-IR pulses and its all-optical detection is enabled by the molecular orientation-induced second harmonic method [J. Phys. Chem. A126, 3732 (2022)10.1021/acs.jpca.2c03237]. This method provides practical means for orientation echo spectroscopy of gas phase molecules and highlights the intriguing underlying physics of coherent rotational dynamics induced by judiciously-orchestrated interactions with both resonant (terahertz) and nonresonant (NIR) fields.

Study of bound and resonant states of NS molecule in the R-matrix approach

The bound and resonance states along with corresponding autoionization widths for nitrogen sulphide (NS) molecule are determined using electron NS+ cation scattering calculations. The calculations are performed for 2Σ+, 2Π and 2Δ total symmetries using the ab initio R-matrix method for both bound and continuum states. Calculations are performed on a grid of 106 points for internuclear separations between 1.32 and 3 Å. The resonance states yield dissociative potential curves which, when considered together with their widths, provide input for models of different electron-cation collision processes including dissociative recombination (DR), and rotational and vibrational excitation. Curves and couplings which will lead directly to DR are identified.

An accurate set of H3O+ − H2 collisional rate coefficients for non-LTE modelling of warm interstellar clouds

ABSTRACT Hydronium (H3O+) was first detected in 1986 in interstellar molecular clouds. It was reported in many Galactic diffuse and dense regions, as well as in extragalactic sources. H3O+ plays a major role both in interstellar oxygen and water chemistry. However, despite the large number of H3O+ observations, its collisional excitation was investigated only partially. In this work, we study the state-to-state rotational (de-)excitation of ortho- and para-H3O+ in collisions both with ortho- and para-H2. The cross sections are calculated within the close-coupling formalism using a highly accurate potential energy surface developed for this system. The rate coefficients are computed up to a kinetic temperature of 300 K. Transitions between the lowest 21 rotation-inversion states were studied for para-H3O+, and the lowest 11 states for ortho-H3O+, i.e. all levels with rotational energies below 430 K (∼300 cm−1) are considered. In order to estimate the impact of the new rate coefficients on the astrophysical models for H3O+, radiative transfer calculations were also carried out. We have examined how the new collisional data affect the line intensities with respect to older data previously used for the interpretation of observations. By analysing all detected transitions we find that our new, accurate rate coefficients have a significant impact (typically within a factor of 2) on radiation temperatures, allowing more accurate estimation of column densities and relative abundances of hydronium, especially in warm molecular clouds, paving the path towards better interpretation of interstellar water and oxygen chemistry.

Imaging the Photodissociation Dynamics and Fragment Alignment of CH2BrI at 193 nm.

The photodissociation dynamics and photofragment alignment of bromoiodomethane (CH2BrI) have been studied at 193 nm using a double experimental and theoretical approach. In addition, the ultraviolet (UV)-vacuum ultraviolet (VUV) absorption spectrum of gas phase CH2BrI has been measured in the photon energy range of 5-11 eV using the VUV Fourier transform spectrometer (FTS) at the VUV beamline DESIRS of the synchrotron SOLEIL facility. The slice imaging technique in combination with resonance enhanced multiphoton ionization (REMPI) detection of the Br(2PJ) and I(2PJ) (with J = 3/2 and 1/2 for Br/I and Br*/I*, respectively) atomic photofragments have been used to produce experimental translational energy and angular distributions, which were analyzed to deliver, on one hand, the partitioning of the available energy among the different degrees-of-freedom of the photofragments and, on the other, the photofragment polarization in terms of aqk(p) alignment parameters. The experimental measurements were rationalized in terms of high-level ab initio calculations of vertical excitation energies, transition dipole moments and potential energy curves (PECs) along different reaction coordinates to provide a complete picture of the photodissociation dynamics. The results indicate that for excitation at 193 nm, prompt C-X cleavage (with X being either halogen atom, Br or I) competes with fast internal conversion and consequent stochastic dissociation in lower electronic states. In the case of the CH2Br + I(2P3/2)/I*(2P1/2) channels, the dynamics are greatly biased toward the stochastic dissociation process due to both the particular PECs landscape and the unfavored excitation of the CH2BrI ensemble with respect to the C-I molecular axis at this excitation energy. The ab initio PECs provide a tentative path for the fast dissociation process in either case. For the C-Br bond breakage, excitation to the 13A' electronic state and predissociation through the 11A'/11A″ or 12A'/12A″ states, leading to direct dissociation through the 10A'/9A″ states, appear as the most consistent dynamics. For the C-I channel, predissociation does not become a reliable possibility and a fast internal conversion may precede dissociation through the repulsive 6A'/6A″ and 4A'/4A″ states. The large content of rotational and vibrational excitation of the polyatomic cofragments is justified through the soft impulsive model and the geometrical changes produced along the dissociation pathway. Strikingly, the aqk(p) alignment parameters obtained for the Br(2P3/2) and I(2P3/2) photoproducts indicate that the rotational angular momentum of the CH2X (X = I or Br) cofragment appears highly constrained along the recoil direction. Finally, this work presents a highly plausible explanation for the branching ratio of secondary dissociation processes in the photodynamics of CH2BrI at 193 nm.

Collaborative control of branching ratio in the O + HO2 → OH + O2 reaction via vibrational and rotational excitation

AbstractTo understand the effect of different vibrational and rotational modes of reactant to enhance the reactivity of the O + HO2 → OH + O2 reaction, we revisited this important atmospheric reaction. We report here a quasi‐classical trajectory (QCT) study of the reaction dynamics on a recently developed full‐dimensional potential energy surface (PES). Our previous work has indicated that this reaction has two pathways, the H abstraction (HA) channel and the O abstraction (OA) channel, which lead to totally different product energy distribution. In this work, we identified that the vibrational excitation of the OH stretching (v1) mode of HO2 is the switch of the HA channel at low collision energy; meanwhile, the rotational excitation can also greatly change the branching ratio of the two pathways. With the excitation of v1 mode, the original negligible HA channel controlled by the tight transition state becomes quite important. This work presents an approach to control the branching ratio via collaboration between vibrational and rotational excitation and will enrich the knowledge of the O + HO2 reaction in atmospheric chemistry and physics.

Finite element level validation of an anisotropic hysteresis model for non-oriented electrical steel sheets

This paper presents the finite element level validation of the anisotropic Jiles–Atherton hysteresis model. Numerical analysis of a round rotational single sheet tester is performed using the 2D finite element method. Anisotropic extension of the Jiles–Atherton hysteresis model is coupled with the 2D finite element method. The finite element simulations are performed for the cases when the magnetic field alternates and rotates in the lamination plane. The simulated results for alternating and rotational flux density excitations agree with the measured data. The measured data used in this paper corresponds to the M400-50A nonoriented silicon steel.

A Systematic Calibration Modeling Method for Redundant INS with Multi-Sensors Non-Orthogonal Configuration.

Because of the non-orthogonal configuration of multi-sensors, the redundant inertial navigation system (INS) has a more complex error model compared with the traditional orthogonal INS, and the complexity of sensors configuration also increases the difficulty of error separation. Based on sufficient analysis of the error principle of redundant IMUs, a generalized high-accuracy calibration modeling method which is suitable for filtering method systematic calibration is summarized in this paper, and it has been applied to an RIMU prototype consisting of four ring laser gyros (RLGs) and four quartz accelerometers. Through the rotational excitation of the three-axis turntable in the laboratory, the high-precision filtering method systematic calibration of the RIMU is achieved, and static navigation and dynamic vehicle test experiments are also carried out. The experimental results reflect that the positioning accuracy can be obviously improved by using this new systematic calibration error model and the validity of this modeling method is also verified.

Accurate time-dependent wave packet calculation for the reaction of Al(2P) + H2[formula omitted] on the AlH2(12A′) surface

The time-dependent wave packet calculation of the Al(2P) + H2X1∑g+ → H(2S) + AlHX1∑+(X1Σ+) reaction is studied on the precise global potential energy surface of AlH2(12A′). The collision energy dependence of reaction probabilities under different total angular momentum is discussed detailedly. The emphasis is on the exploration of different dynamical behaviors calculated by Coriolis coupling and centrifugal sudden approximation, which makes integral scattering cross section calculated by Coriolis coupling has a smaller oscillation intensity clearly. Moreover, the reaction is enhanced strongly by vibration excitation of H2 molecule but only weakly by rotation excitation due to the late barrier.

An electromagnetic rotary-translational motion energy harvester enabled by magnetic-regulated magnetic sphere

This paper describes an electromagnetic energy harvester that uses a rotary-translational magnetic regulation system to convert vibration energy into electrical power. The system consists of a springless magnetic sphere multiple rolling in a cavity and multiple magnetic disks evenly embedded in the cavity. Multiple magnetic disks are arranged with alternating magnetic pole shifts, with the goal of modulating the traditional erratic rolling of the magnetic sphere into a multi-circle regular movement with the change of the magnetic disk’s magnetic pole. Faraday’s law is used to create electromotive forces in coils due to the rotating magnetic moment. The output voltages are measured and analyzed using motion and rotation excitation, parallel, and series coil connections. Experiments on the magnetic sphere with and without magnetic regulation are carried out using a manufactured apparatus. The magnetic sphere with magnetic regulation has periodic and regular output characteristics, according to the results of the experiments. A prototype electromagnetic energy harvester can charge a 0.47 F capacitor to more than 0.40 V in less than 450 s under rotating excitation. The device's energy and effective average power are calculated to be 10.62 J and 23.60 mW. • Random motion in any orientation can be transformed into a multi-circle rotational motion. • The sphere in roll motion with the magnetic disks' regulating system has been used to harvest ambient vibration. • It is the appropriate choice for the rotation energy harvesting, which gets rid of the limited degrees of freedom.

Divergence of phonon angular momentum driven by temperature and strain

Phonon angular momentum (PAM) may exhibit exotic temperature dependence as it is sensitive to the phonon lifetime. Constant phonon-lifetime approximation fails to depict such behavior. Here, we study the PAM of AlN, GaN, and graphenelike boron nitride (g-BN) monolayer with full consideration of phonon lifetime using first-principles calculations. We show that wurtzite AlN and GaN acquire divergent PAM at low temperatures from their lowest-lying phonon branches. The g-BN monolayer, on the other hand, does not have finite PAM at equilibrium structure. Rather, it shows intriguing strain dependence on PAM; the compressive strain greater than the critical size generates divergent PAM at low temperatures due to the divergent lifetime of TA phonons. As PAM couples with rotational excitations in solids associated with charge, spin, or electromagnetic fields, our study demonstrates a possibility of mechanical and thermal engineering of such excitations.

Circularly Polarized Antenna Array with Decoupled Quad Vortex Beams.

Achieving multiple vortex beams with different modes in a planar microstrip array is pivotal, yet still extremely challenging. Here, a hybrid method combining both Pancharatnam−Berry (PB) phase that is induced by the rotation phase and excitation phase of a feeding line has been proposed for decoupling two orthogonal circularly polarized vortex beams. Theoretical analysis is derived for array design to generate quad vortex beams with different directions and an arbitrary number of topological charges. On this basis, two 8 × 8 planar arrays were theoretically designed in an X band, which are with topological charges of l1 = −1, l2 = 1, l3 = −1, and l4 = 1 in Case I and topological charges of l1 = −1, l2 = 1, l3 = −1, and l4 = 1 in Case II. To further verify the above theory, the planar array in Case I is fabricated and analyzed experimentally. Dual-LP beams are realized by using rectangular patch elements with two orthogonally distributed feeding networks on different layers based on two types of feeding: proximity coupling and aperture coupling. Both the numerical simulation and experimental measurement results are in good agreement and showcase the corresponding quad-vortex-beam characteristics within 8~12 GHz. The array achieves a measured S11 < −10 dB and S22 < −10 dB bandwidth of more than 33.4% and 29.2%, respectively. In addition, the isolation between two ports is better than −28 dB. Our strategy provides a promising way to achieve large capacity and high integration, which is of great benefit to wireless and radar communication systems.

ExoMol line lists – XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)

ABSTRACT Any future detection of the calcium monohydroxide radical (CaOH) in stellar and exoplanetary atmospheres will rely on accurate molecular opacity data. Here, we present the first comprehensive molecular line list of CaOH covering the $\tilde{A}\, ^2\Pi$–$\tilde{X}\, ^2\Sigma ^+$ rotation-vibration-electronic and $\tilde{X}\, ^2\Sigma ^+$–$\tilde{X}\, ^2\Sigma ^+$ rotation-vibration bands. The newly computed OYT6 line list contains over 24.2 billion transitions between 3.2 million energy levels with rotational excitation up to J = 175.5. It is applicable to temperatures up to T = 3000 K and covers the 0–35 000 cm−1 range (wavelengths λ &amp;gt; 0.29 μm) for rotational, rotation-vibration and the $\tilde{A}\, ^2\Pi$–$\tilde{X}\, ^2\Sigma ^+$ electronic transitions. The strong band around 16 000 cm−1 (λ = 0.63 μm) is likely to be of interest in future astronomical observations, particularly in hot rocky exoplanets where temperatures can become extremely high. The OYT6 line list has been generated using empirically refined $\tilde{X}\, ^2\Sigma ^+$ and $\tilde{A}\, ^2\Pi$ state potential energy surfaces, high-level ab initio transition dipole moment surfaces, and a rigorous treatment of both Renner–Teller and spin-orbit coupling effects, which are necessary for correctly modelling the CaOH spectrum. Post-processing of the CaOH line list has been performed so as to tailor it to high-resolution applications, i.e. by replacing calculated energy levels with more accurate empirically derived values (where available), hence improving the accuracy of the predicted line positions in certain regions. The OYT6 line list is available from the ExoMol data base at www.exomol.com and the CDS astronomical data base.

Molecular Dynamics Simulations of Nitric Oxide Scattering Off Graphene.

We performed classical molecular dynamics simulations to model the scattering process of nitric oxide, NO, off graphene supported on gold. This is motivated by our desire to probe the energy transfer in collisions with graphene. Since many of these collision systems comprising of graphene and small molecules have been shown to scatter non-reactively, classical molecular dynamics appear to describe such systems sufficiently. We directed thousands of trajectories of NO molecules onto graphene along the surface normal, while varying impact position, but also speed, orientation, and rotational excitation of the nitric oxide, and compare the results with experimental data. While experiment and theory do not match quantitatively, we observe agreement that the relative amount of kinetic energy lost during the collision increases with increasing initial kinetic energy of the NO. Furthermore, while at higher collision energies, all NO molecules lose some energy, and the vast majority of NO is scattered back, in contrast at low impact energies, the fraction of those nitric oxide molecules that are trapped at the surface increases, and some NO molecules even gain some kinetic energy during the collision process. The collision energy seems to preferentially go into the collective motion of the carbon atoms in the graphene sheet.

The effect of water and electron collisions in the rotational excitation of HF in comets

ABSTRACT We present the first set of rate coefficients for the rotational excitation of the 7 lowest levels of hydrogen fluoride (HF) induced by collision with water molecules, the dominant collider in cometary comas, in the 5–150 K temperature range. The calculations are performed with a quantum statistical approach from an accurate rigid rotor ab initio interaction potential. Rate coefficients for excitation of HF by electron-impact are also computed, within the Born approximation, in the 10–10 000 K temperature range. These rate coefficients are then used in a simple non-local thermodynamic equilibrium (non-LTE) model of a cometary coma that also includes solar radiative pumping and radiative decay. We investigate the range of H2O densities that lead to non-LTE populations of the rotational levels of HF. We show that to describe the excitation of HF in comets, considering collisions with both water molecules and electrons is needed as a result of the large dipole of HF.

Hyperfine resolved rate coefficients of HC17O+ with H2 (j = 0)

ABSTRACT The formyl cation (HCO+) is one of the most abundant ions in molecular clouds and plays a major role in the interstellar chemistry. For this reason, accurate collisional rate coefficients for the rotational excitation of HCO+ and its isotopes due to the most abundant perturbing species in interstellar environments are crucial for non-local thermal equilibrium models and deserve special attention. In this work, we determined the first hyperfine resolved rate coefficients of HC17O+ in collision with H2 (j = 0). Indeed, despite no scattering calculations on its collisional parameters have been performed so far, the HC17O+ isotope assumes a prominent role for astrophysical modelling applications. Computations are based on a new four dimensional (4D) potential energy surface obtained at the CCSD(T)-F12a/aug-cc-pVQZ level of theory. A test on the corresponding cross-section values pointed out that, to a good approximation, the influence of the coupling between rotational levels of H2 can be ignored. For this reason, the H2 collider has been treated as a spherical body and an average of the potential based on five orientations of H2 has been employed for scattering calculations. State-to-state rate coefficients resolved for the HC17O+ hyperfine structure for temperature ranging from 5 to 100K have been computed using recoupling techniques. This study provides the first determination of HC17O+–H2 inelastic rate coefficients directly computed from full quantum close-coupling equations, thus supporting the reliability of future radiative transfer modellings of HC17O+ in interstellar environments.