O2 Collisions Research Articles

Rate coefficients for C and O2 reactive collisions relevant to interstellar clouds from QCT and machine learning

The chemical reactions between certain interstellar molecules are exothermic in nature and barrierless in the entrance channel, allowing these reactions to occur rapidly even at low astronomical temperatures, e.g., C and O2 interaction. Obtaining detailed rovibrational transition parameters for the reaction between C and O2, such as state-selected rate coefficients, is crucial for studying the associated atmospheric and astronomical environments. Hence, this work presents an approach that combines quasi-classical trajectory calculations with machine learning techniques based on Neural Network (NN) and Gaussian Process Regression (GPR) to determine state-selected rate coefficients. Employing this approach, we significantly reduced the computational requirements while simultaneously obtaining the accurate state-selected reaction cross sections and rate coefficients for the collision of C and O2. Both the NN-based and GPR-based models established in this work accurately predict the results calculated from explicit numerical calculations in the explored temperature range of 50–1500 K, achieving a coefficient of determination R2 > 0.96. Most importantly, the current work provides the most comprehensive dataset of rovibrational rate coefficients of v = 0–4, j = 0–70 → v′ = 0–15 for the astrophysical modeling of the C–O2 collision system.

Influence of Singlet Oxygen in H + O2 Collision Reaction.

The collision reaction of H + O2 = OH + O is a pivotal step in combustion. To investigate the influence of singlet oxygen on this reaction, we computed potential energy surfaces (PESs) for all six lowest states using high-level ab initio methods and coupled them with embedded atom neural network (EANN) fitting. By integrating quasi-classical trajectory (QCT) with trajectory surface hopping (TSH) based on the fitted PESs, we simulated the dynamics of both ground- and excited-states to derive the reaction rate constants for the forward and reverse processes. The results reveal that the forward reaction facilitates radical generation, promoting combustion reactions. Furthermore, calculations of reverse reaction rate constants indicate that all electronic states ultimately yield ground-state oxygen, leading to radical deactivation and exerting an inhibitory effect on combustion processes.

Gaussian Process Regression for State-to-State Integral Cross Sections: The Case of the O + O2 Collision Dissociation Reactions.

Research on hypersonic vehicles has become increasingly important worldwide in recent years. However, accurately simulating the dynamics of the nonequilibrium high-temperature reactions that are in the hypersonic flow around the vehicles presents a significant challenge as a large number of states and transitions are accessible even for the smallest atom-diatom reaction systems. It is quite difficult, sometimes even impossible, to exhaustively investigate all relevant combinations or determine high-dimensional analytical representations for the state-to-state reaction probabilities. In this study, we used Gaussian process regression (GPR) to fit a model based on only 807 QCT data for training. The confidence interval of the GPR prediction and the Kullback-Leibler (KL) divergence were used to help minimize the sampling amount of data for fitting the converged GPR model. The model aims to predict the state-to-state integral cross section (ICS) of the O + O2 → 3O dissociation reaction under random initial conditions (Et, v, j). In total, it took almost a month to obtain this converged GPR model, but it took only a few seconds to predict the ICS value for any initial condition. For 330 initial conditions not included in the training set, the mean-square error (MSE) between the QCT-calculated ICSs and the GPR-predicted ones is only 0.08 Å2 and the R2 is 0.9986, indicating that the GPR model can replace the direct expensive QCT calculation with high accuracy. Finally, we calculated the equilibrium dissociation rate coefficients based on the StS ICS values predicted by the GPR model, and the results were in good agreement with available experimental and theoretical results. Thus, this study provides an effective and accurate approach to the extensive direct state-to-state reaction dynamic calculations.

Scattering of diatomic molecules from graphite

In the last years, state-to-state molecular dynamics simulations of some basic elementary processes, occurring at the gas–surface interface in a wide range of temperatures and collision energies, have been performed by adopting new potential energy surfaces. In this contribution, our attention is mostly addressed to the role of long-range forces, determining the physisorption of gaseous molecules on the surface. Such forces, formulated in terms of the improved Lennard–Jones interaction potential model, control the formation of precursor or pre-reactive state that plays a crucial role in the dynamical evolution of molecules impinging on the surface in the range of low–intermediate collision kinetic energies. The study focuses on the collisions of H2, O2, N2 and CO, initially in their ground and excited vibro-rotational levels, on a graphite surface. The resulting dispersion coefficients, which control the capture of impinging molecules, are compared and found in good agreement with those available in the literature. New selectivity and peculiarities of scattered molecules, crucial to control the kinetics of elementary chemical processes occurring at the gas–surface interfaces under thermal and sub-thermal conditions, of interest in different applied fields, are highlighted.Graphic abstract

Experimental and Theoretical Studies of Hyperthermal N + O2 Collisions.

The dynamics of hyperthermal N(4S) + O2 collisions were investigated both experimentally and theoretically. Crossed molecular beams experiments were performed at an average center-of-mass (c.m.) collision energy of ⟨Ecoll⟩ = 77.5 kcal mol-1, with velocity- and angle-resolved product detection by a rotatable mass spectrometer detector. Nonreactive (N + O2) and reactive (NO + O) product channels were identified. In the c.m. reference frame, the nonreactively scattered N atoms and reactively scattered NO molecules were both directed into the forward direction with respect to the initial direction of the reagent N atoms. On average, more than 90% of the available energy (⟨Eavl⟩ = 77.5 kcal mol-1) was retained in translation of the nonreactive products (N + O2), whereas a much smaller fraction of the available energy for the reactive pathway (⟨Eavl⟩ = 109.5 kcal mol-1) went into translation of the NO + O products, and the distribution of translational energies for this channel was broad, indicating extensive internal excitation in the nascent NO molecules. The experimentally derived c.m. translational energy and angular distributions of the reactive products suggested at least two dynamical pathways to the formation of NO + O. Quasiclassical trajectory (QCT) calculations were performed with a collision energy of Ecoll = 77 kcal mol-1 using two sets of potential energy surfaces, denoted as PES-I and PES-II, and these theoretical results were compared to each other and to the experimental results. PES-I is a reproducing kernel Hilbert space (RKHS) representation of multireference configurational interaction (MRCI) energies, while PES-II is a many-body permutation invariant polynomial (MB-PIP) fit of complete active space second order perturbation (CASPT2) points. The theoretical investigations were both consistent with the experimental suggestion of two dynamical pathways to produce NO + O, where reactive collisions may proceed on the doublet (12A') and quartet (14A') surfaces. When analyzed with this theoretical insight, the experimental c.m. translational energy and angular distributions were in reasonably good agreement with those predicted by the QCT calculations, although minor differences were observed which are discussed. Theoretical translational energy and angular distributions for the nonreactive N + O2 products matched the experimental translational energy and angular distributions almost quantitatively. Finally, relative yields for the nonreactive and reactive scattering channels were determined from the experiment and from both theoretical methods, and all results are in reasonable agreement.

Low temperature state-to-state vibrational kinetics of O + N2(v) and N + O2(v) collisions

Starting from an equilibrium initial condition at 3000 K, the non-equilibrium vibrational kinetics of a 500 K atmospheric pressure N2/N/O2/O/NO mixture is investigated with a zero-dimensional time-dependent numerical solver. Attention is devoted to the O + N2(v) and N + O2(v) collisions, thanks to new QCT state-to-state rates from the literature. The Zeldovich and the dissociation–recombination reactions are considered; for the N + O2(v) collisions the inelastic vT processes are considered too. Interpolation formulae of the corresponding rates are proposed.The mixture behaviour depends on the combined effects of the different processes, however under the conditions adopted the forward second Zeldovich reaction switches on the kinetics towards a new equilibrium.The aim of the present study is to open the door to more complex applications of plasmas in the fields of the plasma medicine, the fertilizers production and, more in general, of the nitrogen fixation.

The water vapor foreign continuum in the 8100-8500 cm−1 spectral range

In the Earth's atmosphere, the foreign absorption continuum of water vapor is due to the interaction of water molecules with other atmospheric gases (mostly N2 and O2). Following our study of the self-continuum in the high energy edge of the 1.25 µm transparency window (Korovela et al, J. Quant. Spectrosc. Radiat. Transfer 286 (2022) 108206), we report here the first room temperature measurements of water vapor foreign continuum in the same spectral region. Foreign continuum cross-sections, CF, are derived at several selected spectral points between 8120 and 8500 cm−1 for humidified nitrogen, humidified oxygen and humidified air (10000 ppm of H2O). The absorption signal is measured by cavity ring-down spectroscopy (CRDS) using pressure ramps up to 750 Torr. While the measured total continuum absorption follows nicely the expected quadratic dependence versus the total pressure, the uncertainty on the retrieved weak foreign continuum is strongly affected by other contributions which have to be subtracted from the measured absorption (far wings of the resonance lines, O2 collision induced absorption, self-continuum, Rayleigh scattering). The obtained H2O-air and H2O-N2CF cross-section values are found to be comparable while the H2O-O2CF values appear to be significantly smaller. Overall, the retrieved CF values for H2O-air mixture validate the MT_CKD model in the considered region.

Diabatic potential energy surfaces and semiclassical multi-state dynamics for fourteen coupled 3 A′ states of O3

Dissociation and energy transfer in high-energy collisions of O2 play important roles in simulating thermal energy content and heat flux in flows around hypersonic vehicles. Furthermore, atomic oxygen reactions on the vehicle surface are an important contributor to heat shield erosion. Molecular dynamics modeling is needed to better understand the relevant rate processes. Because it is necessary to model the gas flows in high-temperature shock waves, electronically excited states of O2 and O can be populated, and molecular dynamics simulations should include collisions of electronically excited species and electronically nonadiabatic collisions. This requires potential energy surfaces and state couplings for many energetically accessible electronic states. Here we report a systematic strategy to calculate such surfaces and couplings. We have applied this method to the fourteen lowest-energy potential energy surfaces in the 3 A′ manifold of O3, and we report a neural-network fit to diabatic potential energy matrix (DPEM). We illustrate the use of the resulting DPEM by carrying out semiclassical dynamics calculations of cross sections for excitation of O2 in 3 A′ collisions with O at two collision energies; these dynamics calculations are carried out by the curvature-driven coherent switching with decay of mixing method.

State-Specific Dynamic Study of the Exchange and Dissociation Reaction for O(3P) and O2($${}^{3}\Sigma _{g}^{ - }$$) Collision by Quasi-Classical Trajectory

State-Specific Dynamic Study of the Exchange and Dissociation Reaction for O(3P) and O2($${}^{3}\Sigma _{g}^{ - }$$) Collision by Quasi-Classical Trajectory

N + O2(v) collisions: reactive, inelastic and dissociation rates for state-to-state vibrational kinetic models

The reactive, inelastic and dissociation vibrationally-detailed rate coefficients of the N + O2 collision processes, previously calculated by means of a QCT method, have been interpolated as a function of the initial and final vibrational levels and of the temperature, in the range 1000–20000 K. These rates have been implemented in a N2/N/O2/O/NO mixture state-to-state kinetic model. The model has been tested in a couple of applications. The first consists in its time evolution, for 10−3 s, from an equilibrium composition at 4000/3000 K towards a new composition obtained by suddenly decreasing the temperature to 1000 K. This is a preliminary study that could open the way to a new approach in the investigation of some biomedical applications governed by plasma sources at atmospheric pressure. The second test regards the boundary layer formed around the nose of a hypersonic vehicle in the framework of the fast transportation and space tourism applications.

Stereo-dynamical effects in chemi-ionization reactions of atmospheric O2 and N2 molecules promoted by collisions with Ne*(3P2,0) atoms

This letter focuses on general aspects of the stereodynamics of chemi-ionization reactions, triggered by collisions of O2 and N2 molecules with metastable neon atoms. Basic characteristics of the long-range intermolecular forces involved, some of chemical and others of physical origin, suggest that the weakly bound precursor state, determining the reaction transition state structure and stability, is rather different. Fundamental reaction selectivities are clarified, highlighting differences in the: i) optical potential whose real and imaginary parts must be interdependent; ii) polarizability, quadrupolar moments and orbital representation of the molecules involved, which allow to lay the foundations for future more in-depth investigations.

Potential energy surfaces for high-energy N + O2 collisions.

Potential energy surfaces for high-energy collisions between an oxygen molecule and a nitrogen atom are useful for modeling chemical dynamics in shock waves. In the present work, we present doublet, quartet, and sextet potential energy surfaces that are suitable for studying collisions of O2(3Σg -) with N(4S) in the electronically adiabatic approximation. Two sets of surfaces are developed, one using neural networks (NNs) with permutationally invariant polynomials (PIPs) and one with the least-squares many-body (MB) method, where a two-body part is an accurate diatomic potential and the three-body part is expressed with connected PIPs in mixed-exponential-Gaussian bond order variables (MEGs). We find, using the same dataset for both fits, that the fitting performance of the PIP-NN method is significantly better than that of the MB-PIP-MEG method, even though the MB-PIP-MEG fit uses a higher-order PIP than those used in previous MB-PIP-MEG fits of related systems (such as N4 and N2O2). However, the evaluation of the PIP-NN fit in trajectory calculations requires about 5 times more computer time than is required for the MB-PIP-MEG fit.

Ammonia line strengths and N2-, O2-, Ar-, He-, and self-broadening coefficients in the v2 band near 10.4 µm

Scanning-wavelength laser absorption measurements were carried out to determine the line strengths and broadening coefficients due to collisions of N2, O2, Ar, He, and NH3 for 12 ammonia transitions in the Q-branch of the v2 fundamental band near 10.4 µm. The measurements were conducted at 296 K using a high-resolution quantum cascade laser and span the frequency range of 957.5–963.0 cm−1. The absorption features were fitted with a Voigt profile to obtain the spectroscopic parameters. The temperature-dependence of the Ar-broadening coefficients for two transitions, suitable for high-temperature NH3 detection, were measured using a shock tube for the temperature range of 921–1767 K. The reported spectroscopic parameters are useful for developing NH3 detection sensors, especially for high-temperature applications involving chemical reactions.

Vibrational relaxation time measurements in shock-heated oxygen and air from 2000 K to 9000 K using ultraviolet laser absorption

Vibrational relaxation times of oxygen (O2) were measured behind reflected shocks in shock-tube experiments with O2 and nitrogen (N2) collision partners. To determine relaxation times, a tunable ultraviolet laser absorption diagnostic probed time-histories involving the fourth (v″ = 4), fifth (v″ = 5), and sixth (v″ = 6) vibrational levels of the ground electronic state of O2. Taking the ratio of two absorbance time-histories involving different vibrational levels yielded vibrational temperature time-histories that were fit to isolate the relevant vibrational relaxation times. Pure O2 experiments were used to isolate the vibration–translation (VT) relaxation time of O2 with O2. Results for τVTO2–O2 agree with the Millikan and White correlation at temperatures below 4000 K. However, high-temperature data deviate from the Millikan and White correlation, exhibiting a reduced temperature dependence—an observation that remains consistent with previous experimental studies. Additional experiments in 10% and 21% O2 in N2 mixtures were used to isolate both the VT and vibration–vibration (VV) relaxation times of O2 with N2. The data for τVTO2–N2 exceed the Millikan and White correlation by 70% but show reasonable agreement with previous data below 5000 K. High-temperature results again show a reduced temperature dependence, but this study shows longer relaxation times than the previous work. The data for τVVO2–N2 exceed the semi-empirical relation developed by Berend et al. [“Vibration-vibration energy exchange in N2 with O2 and HCl collision partners,” J. Chem. Phys. 57, 3601–3604 (1972)] by 70% but overlap with previous measurements. Due to insensitivity of the chemical system to VV transfer at high temperatures, results for τVVO2–N2 were only measured below 6000 K.

Dynamics Studies of O2 Collision on Pt(111) Using a Global Potential Energy Surface

The dynamics of O2 collision on Pt(111) has been studied by molecular dynamics simulations using a global potential energy surface (PES), which was developed by fitting ∼4800 plane-wave density functional theory points using the permutation invariant polynomial-neural network method. The simulations were performed for the normal and off-normal incidences at a wide range of incident energies and surface temperatures. A generalized Langevin oscillator model was used to incorporate the molecule–surface coupling that plays an important role in this collision process. The trapping probability, final energy distribution, scattering angle distributions of scattered molecules, and the energy transfer to surface distribution were determined and analyzed. The PES shows an activated path to the chemisorption states, as the trapping probability directly increases with incident energy (larger than 0.1 eV) to reach a maximum and then decreases at high incident energy. The trapping probability obviously reduces by raising surface temperature at low incident energy because the initial kinetic energy of molecule is more likely to be dissipated into surface motions than molecular internal ro-vibrational modes. Additional parallel momentum of off-normal incidence leads to a strong suppression of the trapping probability, caused by the energetic corrugation of the lateral barrier heights. The scattering angular distributions are found to be quasispecular and the final translational energy slightly increases with scattering angle deviating significantly from the hard-cube model, indicating the nonconservation of parallel momentum during the collision on the corrugate PES.

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

Inelastic Collisions of O2 with He at Low Temperatures.

Rotationally inelastic collisions of O2 with He in the 10-34 K thermal range are investigated by means of an experimental procedure based on supersonic gas jets probed by Raman spectroscopy. The procedure employs a kinetic master equation (MEQ) that describes the time evolution of the rotational populations of O2 along supersonic jets of O2 and He mixtures. The MEQ is expressed in terms of experimental quantities (number density and rotational populations) measured here, and state-to-state rate coefficients for the O2:He inelastic collisions calculated here, plus those for O2:O2 collisions from the literature. An agreement with the experiments is accomplished for temperatures between 10 and 34 K. Within this thermal range, the role of the fine structure due to electron spin in the collision dynamics of O2 is discussed.

Imaging the nonreactive collisional quenching dynamics of NO (A2Σ+) radicals with O2 (X3Σg -).

Nitric oxide (NO) radicals are ubiquitous chemical intermediates present in the atmosphere and in combustion processes, where laser-induced fluorescence is extensively used on the NO (A2Σ+ ← X2Π) band to report on fuel-burning properties. However, accurate fluorescence quantum yields and NO concentration measurements are impeded by electronic quenching of NO (A2Σ+) to NO (X2Π) with colliding atomic and molecular species. To improve predictive combustion models and develop a molecular-level understanding of NO (A2Σ+) quenching, we report the velocity map ion images and product state distributions of NO (X2Π, v″ = 0, J″, Fn, Λ) following nonreactive collisional quenching of NO (A2Σ+) with molecular oxygen, O2 (X3Σg -). A novel dual-flow pulse valve nozzle is constructed and implemented to carry out the NO (A2Σ+) electronic quenching studies and to limit NO2 formation. The isotropic ion images reveal that the NO-O2 system evolves through a long-lived NO3 collision complex prior to formation of products. Furthermore, the corresponding total kinetic energy release distributions support that O2 collision coproducts are formed primarily in the c1Σu - electronic state with NO (X2Π, v″ = 0, J″, Fn, Λ). The product state distributions also indicate that NO (X2Π) is generated with a propensity to occupy the Π(A″) Λ-doublet state, which is consistent with the NO π* orbital aligned perpendicular to nuclear rotation. The deviations between experimental results and statistical phase space theory simulations illustrate the key role that the conical intersection plays in the quenching dynamics to funnel population to product rovibronic levels.

Doping metal-organic framework with a series of europium-antenna cations: Obviously improved spectral response for O2 gas via long-range energy roll-back procedure

In this paper, a lanthanide cation, Eu(III), was firstly coordinated with a series of organic antenna ligands and then doped into bio-MOF-1 via cation exchange for O2 optical sensing. These organic ligands were supposed to increase dynamic collision probability between O2 molecules and excited probe molecules, so that sensitivity could be increased and response time could be decreased. These composite samples were firstly identified using SEM, XRD, N2 adsorption/desorption and ICP measurement to confirm their microstructure. Then their absorption spectra, emission spectra and emission lifetimes were discussed. It was found that these composite samples showed long emission lifetime up to 595 μs, which ensured enough time for O2 collision. Their O2 sensing performance was discussed via their emission spectra under increasing O2 concentrations. Linear sensing curves were observed for all samples. It was found that a large conjugation plane improved sensitivity and decreased response time since this large conjugation plane increased dynamic collision probability. The sensing mechanism was confirmed as the O2 quenching on long-range energy roll-back from ligand triplet state to bio-MOF-1. The highest sensitivity and the shortest response time were obtained as 6.96, three times higher than literature values, and 12 s, respectively.

Direct molecular simulation of internal energy relaxation and dissociation in oxygen

A variant of the direct simulation Monte Carlo (DSMC) method, referred to as direct molecular simulation (DMS), is used to study oxygen dissociation from first principles. The sole model input to the DMS calculations consists of 12 potential energy surfaces that govern O2 + O2 and O + O2 collisions, including all spin-spatial degenerate configurations, in the ground electronic state. DMS calculations are representative of the gas evolution behind a strong shock wave, where molecular oxygen excites rotationally and vibrationally before ultimately dissociating and reaching a quasi-steady-state (QSS). Vibrational relaxation time constants are presented for both O2 + O2 and O + O2 collisions and are found to agree closely with experimental data. Compared to O2 + O2 collisions, vibrational relaxation due to O + O2 collisions is found to be ten times faster and to have a weak dependence on temperature. Dissociation rate constants in the QSS dissociation phase are presented for both O2 + O2 and O + O2 collisions and agree (within experimental uncertainty) with rates inferred from shock-tube experiments. Both experiments and simulations indicate that the QSS dissociation rate coefficients for O + O2 interactions are about two times greater than the ones for O2 + O2. DMS calculations predict this to be a result of nonequilibrium (non-Boltzmann) internal energy distributions. Specifically, the increased dissociation rate is caused by faster vibrational relaxation, due to O + O2 collisions, which alters the vibrational energy distribution function in the QSS by populating higher energy states that readily dissociate. Although existing experimental data appear to support this prediction, experiments with lower uncertainty are needed for quantitative validation. The DMS data presented for rovibrational relaxation and dissociation in oxygen could be used to formulate models for DSMC and computational fluid dynamics methods.