Energy Transfer In Molecular Collisions Research Articles

Simulation of 1D atmospheric pressure dielectric barrier discharge in argon

This work aims at modelling an atmospheric-pressure homogeneous barrier discharge in argon, using a time-dependent 1D fluid model coupled to the electric field and plasmo-chemical kinetic equations. The model is chosen to mimic a discharge when a sinusoidal 1 kV voltage at 10 MHz is applied to the terminals. Energy and mass transfer are considered for a macroscopic fluid representation, while energy transfer in molecular collisions and chemical reactions is treated at the microscopic level. The macroscopic model is represented by a set of coupled partial differential equations. Microscopic effects are studied within a discrete model for electronic and molecular collisions in the frame of ZDPlasKin, a plasma modelling numerical tool. The BOLSIG+ solver is employed in solving the electronic Boltzmann equation. An operator splitting technique is used to separate microscopic and macroscopic models. The spatial and temporal evolution of such species and electron transport parameters are presented and discussed.

Rotational energy transfer in the collision of N2O with He atom.

The quantum state-to-state rotationally inelastic quenching of N2O by colliding with a He atom is studied on an abinitio potential energy surface with N2O lying on its vibrational ground state. The cross sections for collision energies from 10-6-100cm-1 and rate constants from 10-5-10K are calculated employing the fully converged quantum close-coupling method for the quenching of the j = 1-6 rotational states of N2O. Numerous van der Waals shapes or Feshbach resonances are observed; the cross sections of different channels are found to follow the Wigner scaling law in the cold threshold regime and may intersect with each other. In order to interpret the mechanism and estimate the cross sections of the rotational energy transfer, we propose a minimal classical model of collision between an asymmetric double-shell ellipsoid and a point particle. The classical model reproduces the quantum scattering results and points out the attractive interactions and the potential asymmetry can affect the collision process. The resulting insights are expected to expand our interpretations of inelastic scattering and energy transfer in molecular collisions.

Energy transfer upon collision of selectively excited CO2 molecules: State-to-state cross sections and probabilities for modeling of atmospheres and gaseous flows.

Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO2 characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO2 + CO2 collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO2 structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7.

Collision-induced Energy Transfer and Bond Dissociation in Toluene by H2/D2

) but increase exponentially with rising vibrational excitation. Intramolecularenergy flow between the excited C-H bonds occurring on a subpicosecond timescale is responsible for the bonddissociation. Key Words : Collision-induced, Dissociation, Intramolecular energy flowIntroductionStudies on the rates and mechanisms of energy transfer inmolecular collisions are critical to understanding elementaryprocesses which play a vital role in chemical reactions.

Asymptotic expansions of time-correlation functions for energy transfer in molecular collisions

Asymptotic expansions of time-correlation functions for energy transfer in molecular collisions

VT energy transfer in molecular collisions: An algebraic approach

A study of the vibration-translation energy transfer in a collinear atom-Morse oscillator collision is made using the operator algebra associated with the Morse potential. Numerical results are presented for the collision between a helium atom and an H2 molecule.

Do vectors point the way to understanding energy transfer in molecular collisions?

This tutorial review examines the proposition that vector properties reveal more about the underlying potential energy surfaces controlling the inelastic exchange of energy in intermolecular collisions than conventional scalar measurements. Exciting recent experimental progress is summarized in the form of six selected cases studies. The new information that has been extracted is compared with the predictions of complementary theory. Likely future prospects and promising avenues for further progress are discussed. The treatment should appeal to all those with interests in the forces governing intermolecular interactions, especially in gas-phase collisions.

Modeling energy transfer in molecular collisions: Statistical theory versus experiment for highly excited toluene and azulene

The recent development and application of the method of kinetically controlled selective ionization has produced detailed and reliable data on the collisional energy transfer kernel P(E′,E) entering master equation theories of unimolecular reaction rates. Here we test the ability of our partially ergodic collision theory (PECT) to predict the functional form of the observed kernel leaving only one parameter, the first moment of the distribution 〈ΔE〉, to be input from other sources. The data explored here include two reactant molecules, toluene and azulene, in collisions with 18 and 8 medium molecules, respectively, ranging from inert gas atoms to n-heptane. The initial energy of the reactant molecule is varied from 10 000 cm−1 to 49 000 cm−1 and 30 000 cm−1, respectively. The energy transfer efficiency βE is about one-tenth of its ergodic collision limit of unity. The PECT is found to fit the monoexponential form of the kernel determined from the experimental data over a broad range of initial energies E including tail regions of very low probability. A minor but systematic deviation is observed for nearly elastic collisions of large medium molecules. The functional fit is good enough to effectively allow the three parameters of the monoexponential experimental kernel to be replaced by a single parameter representing energy transfer efficiency.

Statistical model of energy transfer in molecular collisions: De-energization of highly excited toluene

Recent experimental data on the collisional de-energization of toluene from initial energies of between 10 000 and 49 000 cm−1 have been analyzed by the partially ergodic collision theory. The data for 11 different gases were obtained by kinetically controlled selective ionization by Luther and co-workers [J. Chem. Phys. 112, 4076 (2000)] and are of exceptional detail and reliability. The semiempirical PECT model starts from the average energy transferred per collision 〈ΔE〉 and predicts the full transition probability P(E′,E) to good accuracy. The energy transfer efficiency is about a tenth of the ergodic collision limit with only minor dependence on gas molecule or initial toluene energy.

The Maximum Limit of Rotational Energy Transfer in Molecular Collisions and the Hard Ellipsoid Potential Model

The Maximum Limit of Rotational Energy Transfer in Molecular Collisions and the Hard Ellipsoid Potential Model

The hard ellipsoid potential model and the limit of rotational energy transfer in molecular collisions

The effect of angular momentum conservation constraints on the limit of the rotational energy transfer (RET) in a diatomic molecule due to collisions with an atom has been investigated. The importance of the classical limit of the rotational energy transfer, (ΔE)max, predicted by the hard ellipsoid potential model has been found such that it is comparable to a well known parameter |ΔE|*, given by the two-parameter power-gap (PG) “law” and the RET cross sections computed on the real potentials. Numerical equivalence of (ΔE)max and |ΔE|* for various types of potential surfaces over a wide range of potential parameters, collision energy and the mass of the system has been verified. The feasibility of obtaining the difference of the semimajor and semiminor axes of the hard ellipsoid potential from the scattering data and the PG “law” has also been discussed.

Rotational Energy Transfer in Molecular Collisions and Parameters of Power-Gap "Law"

The quantum mechanical integral inelastic cross-sections for the rotation transitions in a diatomic molecule with an atom were computed and analysed by using the empirical power-gap law over a wide range of coliisioii energy. A well-known parameter, ΙΔEΙ*, of the power-gap law was estimated by observing a rapid fall of cross-sections for the rotational energy transfer, ΙΔE Ι > ΙΔEΙ*. It was found that ΙΔEΙ* corresponds to classical limit of maximum amount of rotational energy transfer permissible by the angular momentum conservation constraints and the hard ellipsoid potential model provided the hard ellipsoid potential surface is represented by the classical turning point surface of the real potential employed in the computation of cross-sections. Such an agreement is shown to be useful in the determination of the difference of major and minor axes of the intermolecular-potential ellipsoid from the knowledge of the cross-sections and the power-gap law. PACS numbers: 34.50.Ez, 34.50.—s

Quantized vibrational densities of states and ergodic energy transfer in molecular collisions

A simple method of generating quantized ro-vibrational densities of states based only on the thermodynamic data is presented. The result is a smooth function accurate over a wide energy range. Its simple power-law form allows the ergodic collision theory limits of energy-transfer moments to be calculated analytically, revealing the nature and magnitude of the quantum effects.

A generalized intermediate picture of quantal time evolution using operator algebraic methods. Application to translational–vibrational energy transfer in molecular collisions

A method for solving the time-dependent Schrödinger equation in an intermediate picture defined by an effective time-dependent Hamiltonian is discussed. The state function in this intermediate picture is written as a linear combination of time-independent basis functions with time-dependent coefficients. It is shown how to use Lie algebraic methods to build the interaction potential in the intermediate picture and calculate physical observables. The construction of the interaction potential is explicitly discussed in the case of one degree of freedom with a classical coordinate analog. The effective Hamiltonian is obtained by expanding the potential energy function around a reference value of the coordinate. Effective Hamiltonians for He–H2 collisions obtained for equilibrium and average reference values of the vibrational coordinate of H2 are compared and the expansion convergence in the resulting intermediate pictures are discussed.

Approximating relative rotational energy transfer in molecular collisions

The rotational energy transfer (RET) processes taking place in an atom–diatomic gaseous mixture are analysed in detail by carrying out collision dynamical calculations of the relevant state-to-state cross-sections. Approximate schemes for the dynamics are tested along the series of He, Ne and Ar rare gases in collisions with N2 molecules, using the IOS and CS approximate models. The corresponding average relative energy transfer (ARET) is found to be a slow function of collision energy and can be used as an efficiency index for the systems at hand. The IOS approximation, however, grossly overestimates this index especially for the more anisotropic interactions. Other dynamical models, like the hard-ellipsoid impulsive model, are also found to have the same shortcomings as the IOSA scheme. It is therefore concluded that approximate treatments of relative rotational energy-transfer processes are capable of only near quantitative predictions for systems that show very low efficiency for such processes, and fail markedly when larger amounts of energy can be transferred during collisions. The present conclusions will be of use in analysing scattering experiments.

Classical energy transfer in forced oscillator models of inelastic scattering

A compact formalism is presented to solve the classical equations of motion for a general linearly driven parametric oscillator. It is shown that quantum transition probabilities obtained from an operator algebraic technique can be expressed in terms of classical energy transfers. The success and limitations of the DECENT method for vibration–translation energy transfer in molecular collisions is discussed and illustrated numerically in a simple model.

ChemInform Abstract: Dynamics of Dissociation and Energy Transfer in Molecular Collisions with Solid Surfaces.

AbstractReview: (description of results obtained in collaboration between the respective theoretical and experimental groups of authors over the past few years; including molecules such as I2 in collision with single‐crystal surfaces of MgO, diamond, and sapphire ‐ ca. 40 refs.

Dynamics of dissociation and energy transfer in molecular collisions with solid surfaces

Dynamics of dissociation and energy transfer in molecular collisions with solid surfaces

Rotational Energy Transfer in Molecular Collisions. I. Resonant Case

The resonant rotational energy transfer of the type M( J =1)+M( J =0)→M( J =0)+M( J =1) has been studied theoretically. M( J ) is a linear polar molecule with the rotational quantum number J . The impact-parameter PRS (Perturbed Rotational State) and the impact-parameter CC (Close-Coupling) methods are applied. The straight-line trajectory and the pure dipole-dipole interaction are assumed. Validity of these simplifying assumptions is discussed. It is found that the energy transfer cross section becomes very large at low collision velocities and that it increases rapidly as the velocity decreases. The results are applicable to any identical linear polar molecules as long as the basic assumptions stated above are valid. For HF+HF, the theoretical prediction is compatible with the recent experimental findings by Vohralik and Miller at the collision energy 0.15 eV.

Theory of vibrational energy exchange in adsorbed polyatomic molecules

Using an effective mass hamiltonian approach developed in studies of energy transfer in molecular collisions, we derive a simple theory of vibrational energy exchange in adsorbed polyatomic molecules. As an application, the vibrational relaxation of CH3Cl and CD3Cl adsorbed on solid Ar is discussed, and the most important accepting modes in the energy relaxation of the ν4 mode are predicted. Possibilities to study the problem experimentally are also discussed briefly.