Energy Exchange Probability Research Articles

"IKKI ATOMLI GAZLARDA TEBRANMA-ILGARILANMA ENERGIYA ALMASHINISH EHTIMOLLIGINI HISOBLASH"

"IKKI ATOMLI GAZLARDA TEBRANMA-ILGARILANMA ENERGIYA ALMASHINISH EHTIMOLLIGINI HISOBLASH"

"IKKI ATOMLI GAZLARDA TEBRANMA-ILGARILANMA ENERGIYA ALMASHINISH EHTIMOLLIGINI HISOBLASH"

"IKKI ATOMLI GAZLARDA TEBRANMA-ILGARILANMA ENERGIYA ALMASHINISH EHTIMOLLIGINI HISOBLASH"

Effect of ambient gas pressure on characteristics of air plasma induced by nanosecond laser

The ambient gas pressure has an important influence on the laser induced plasma characteristics. The effects of gas pressure on the characteristics of air plasma induced by nanosecond laser are studied by using the optical emission spectroscopy, and the relationship between the gas pressure and the spectral intensity, and between electron temperature and electron density of air plasma are discussed. The air gas pressure in chamber is continuously changed in a range from 10 to 100 kPa by using a mechanical pump and measured by using a barometer. The ns laser energy in experiment is fixed at 100 mJ in the whole experiment. The digital delay trigger (Stanford DG535/645) is used to trigger the laser and ICCD synchronously, and the delay and gate time of ICCD are set to be 0 and 5 μs, respectively. The experimental results show that air plasma emission spectrum consists of the line and continuous spectrum, and the spectral intensity of air plasma emission spectrum is dependent on gas pressure in a range from 10 to 100 kPa, and the evolution of atomic spectrum intensity with gas pressure is different from that of ion spectrum intensity. The air density in the region of laser breakdown increases with air pressure increasing, which leads the breakdown probability of air gas to increase, thus resulting in the air plasma spectral intensity increasing. Under the confinement action of the ambient air gas in the expanding region of air plasma, the collision probability and energy exchange probability among particles in the air plasma are both increased, and the trisomic recombination probability of ion-electron-atom is also increased. As a result, the atomic spectral intensity of O Ι 777.2 nm and N Ι 821.6 nm both increase with the air gas pressure increasing, and the spectral intensity is highest at 80 kPa, and then slowly decreases. But the spectral intensity of N II 500.5 nm reaches its maximum value at 40 kPa, and decreases as the pressure becomes greater than 40 kPa. The electron density of the air plasma increases with the air pressure increasing, and the growth rate becomes slow after 80 kPa. The electron temperature of the air plasma reaches a maximum value at 30 kPa. The plasma electron temperature gradually decreases as the pressure becomes greater than 30 kPa. The research results can provide an important experimental basis for studying the laser-induced air plasma characteristics at different altitudes, and also give important technical support for laser atmospheric transmission and atmospheric composition analysis in the future.

Disentangling theorem and scattering functions for long-range coherent tunneling

A closed form of the disentangling theorem is used to derive an exact expression for the quantum mechanical intermediate scattering function describing long-range coherent quantum tunneling. The result applies to a single particle in a large periodic nearest-neighbor tight-binding system in one spatial dimension, with one localized site per unit cell. The result is exact up to the assumption of orthogonal localized states and the substitution of the coordinate operator with a discrete representation diagonal in the on-site basis. The intermediate scattering function is expressed in terms of modified Bessel functions, and consists of a symmetric real part and antisymmetric imaginary part. The real and imaginary parts both exhibit decaying oscillations reflecting the oscillatory dynamics among neighboring sites combined with the long-term spreading of the wave function from any initial site. The imaginary part is significant only when the thermal energy is comparable to or smaller than the width of the tight-binding energy band, and represents quantum recoil or the asymmetry of energy exchange probability in quasielastic scattering from the coherent system. The one-dimensional result is extended, in the form of $\mathbf{k}$-space integrals, to describe the coherent tunneling dynamics in hexagonal and honeycomb systems. The prospects for observing the phenomenology of the analytical line shapes are discussed with respect to the practical implementation of helium-3 surface spin echo spectroscopy.

Влияние интервала движения на вероятность межпоездного обмена энергией рекуперации в метрополитене

Влияние интервала движения на вероятность межпоездного обмена энергией рекуперации в метрополитене

Diffusion of Excitation in GGG:Yb3+ Laser Crystal

The excitation diffusion coefficient DE is measured directly in laser crystals by the optical method of high-frequency dynamic gratings. DE for Gd3Ga5O12:Yb3+ (21 at.%) crystal is found to be 3·10−9 cm3/s at room temperature and 1.2·10−8 cm3/s at 190°C. In KYW:Yb3+ (20 at.%) crystal no excitation diffusion is observed under the same experimental conditions. It is shown that DE is affected by the activator concentration, the temperature, and the probability of radiationless energy exchange between neighboring active impurity ions, which depends on the minimal distance between donor and acceptor.

Application of Langmuir theory of evaporation to the simulation of sample vapor composition and release rate in graphite tube atomizers. Part 1. The model and calculation algorithm

A method is suggested for simulation of transient sample vapor composition and release rate during vaporization of analytes in electrothermal (ET) atomizers for AAS. The approach is based on the Langmuir theory of evaporation of metals in the presence of a gas at atmospheric pressure, which advocates formation of mass equilibrium in the boundary layer next to the evaporation surface. It is suggested in this work that in ET atomizers the release of atoms and molecules from the boundary layer next to the dry residue of the analyte is accompanied by spreading of the layer around the sample droplets or crystals. Thus, eventually, the vapor source forms an effective area associated with a monolayer of the analyte. In particular, for the case of a metal oxide analyte as discussed in the work, the boundary layer contains the species present in thermodynamic equilibrium with oxide, which are metal atoms and dimers, oxide molecules and oxygen. Because of an excess of Ar, the probability of mass and energy exchange between the evolved gaseous species is low, this substantiates independent mass transport of each type of species from the boundary layer and through absorption volume. Diffusion, capture by Ar flow and gas thermal expansion is considered to control vapor transport and release rate. Each specific flow is affected by secondary processes occurring in collisions of the evolved molecules and atoms with the walls of graphite tube. Diffusion of oxygen containing species out of the boundary layer is facilitated by annihilation of oxygen and reduction of oxide on the graphite surface, while interaction of metal vapor with graphite slows down transport of atomic vapor out of the atomizer. These assumptions are used as the basis for the presentation of the problem as a system of first order differential equations describing mass and temperature balance in the atomizer. Numerical solution of the system of equations provides the simulation of temporal composition of the sample constituents in condensed and gas phase in the atomizer according to chemical properties of the analyte and experimental conditions. The suggested approach avoids the description of atomization processes via kinetic parameters such as activation energy, frequency factor, surface coverage or reaction order.

Overall Considerations on the Quenching of PH2(Ã2A1) and New Effects in Collision-Induced V−V Energy Transfer of PH2(X̃2B1; v2‘ ‘ = 1)

The quenching constants of PH2(A(2)A1; v2' = 0 and 1) by H(2)S, NH(3), COS, CHCl(3), and CH4 have been measured. Attempts to correlate these data and those published in previous papers due to other quenchers, with the molecular properties through the Parmenter and co-workers' theory, the Thayer and Yardley's model, and the collision complex formation theory have been made. Measurements of collision-induced deactivation constants of PH2(X(2)B1; v2' ' = 1) by COS, CHCl(3), and CH4 have also been carried out. A reliable linear relationship of the log values of V-V energy exchange probability with the minimum energy mismatch Deltanu between PH2(v2' ' = 1) and the quenchers has been shown. Effects on the V-V transfer efficiency by inversion doubling of NH(3) and by the degenerate vibrational modes of the quencher, which participate in the process, have been evidenced.

Investigation of inductively coupled Ar and CH4/Ar plasmas and the effect of ion energy on DLC film properties

Gas-phase and surface analysis techniques were utilized to investigate the effects of gas-phase species on plasma deposited diamond-like carbon (DLC) thin films. A vacuum system was built to perform Langmuir probe and energy analysis-based mass spectrometry measurements to characterize the gas-phase of low pressure, 13.56 MHz inductively coupled plasma molecular beams. Low-energy peaks contributed significantly to the total area of the ion energy distributions (IEDs) measured for Ar+ in Ar and CH4/Ar plasmas. In contrast, for all other ions in these systems, the low-energy peaks had a lower contribution to the IEDs as a result of the low probability of energy exchange via ion–neutral collisions. Hydrogenated DLC films were deposited on silicon wafers at different substrate potentials to determine the effect of ion bombardment on film properties. Films were characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and nanoindentation measurements. The hydrogen content, surface roughness and deposition rate decreased, whereas the hardness of the films increased when a negative bias voltage was applied. These results demonstrate that ion energy has a significant effect on the composition and morphology of plasma deposited DLC films.

DSMC Simulation of Parallel, Oblique and Normal Free Jet Impingements on a Flat Plate.

In the present paper, jet impingements of gas expanded through an orifice into a vacuum were numerically simulated by using the direct simulation Monte Carlo (DSMC) method. Three types of jet impingement, parallel, oblique and normal, were treated. The parallel and oblique impingements were considered as a three-dimensional problem, whereas normal impingement was treated as an axisymmetric problem. The numerical simulations were carried out using the variable soft sphere (VSS) model for nitrogen. For the energy exchange between translational and rotational modes, the Borgnakke-Larsen model was employed together with the temperature-dependent energy exchange probability of Boyd. Simulated results were compared with Legge’s experiments and a simple impingement model in the range of the reservoir pressures from 0.1×104 to 1.6×104 Pa. The present results agreed well with Legge’s experimental data of pressure and shear stress distributions on a flat plate.

Vibrational nonequilibrium modeling using direct simulation. I - Continuous internal energy

A new class of vibrational nonequilibrium models is introduced for repulsive-attractive intermodular potentials to reproduce on average the relaxation time of Millikan and White over all its domain of validity. Intended to do Monte Carlo simulations, it is proposed at a microscopic scale, in the form of individual probabilities of vibration translation energy exchange p. In this first part the internal energy is assumed to be continuous. The relation linking the required individual probability to the relaxation time to be reproduced is solved thanks to the systematic and exact resolution method, based on the Laplace transformation, that we had proposed earlier. Models previously introduced by Boyd and Bird are found as borderline cases of the present one. Attainment of detailed balance is checked with homogeneous calculations, using the direct simulation Monte Carlo method and the original Borgnakke-Larsen (BL) scheme. Assumption used to develop/? models is discussed in light of numerical results and justified thanks to a recent mathematical study of the BL scheme.

Thermal nonequilibrium modeling using the direct simulation Monte Carlo method: Application to rotational energy

Individual probabilities of energy exchange, appearing in the Boltzmann equation, are proposed. They are developed, for a continuous internal energy, to reproduce, on average, the expected relaxation times. The problem consists in linking the required individual probability to the relaxation time to be reproduced. It is stated, for a given collisional model, from the Boltzmann equation collisional kernel. The underlying assumptions are put forward. A new and systematic resolution method, based on the Laplace transformation, is then presented in detail. Illustrations are proposed, within the frame of the direct simulation Monte Carlo method of Bird, investigating two collisional models. The first one is the widely used variable hard sphere model. Next, an original application to the generalized hard sphere model is also performed. Examples of resolutions are carried out studying rotational relaxation. The rotational models previously developed are included in the results obtained. A new hypothesis used to state the problem is discussed in the light of numerical calculations and of a recent mathematical study.

Temperature dependence of the probability of vibrational energy exchange between the stretching modes in H 2O/D 2O + Ar collisions

The vibrational energy exchange between the stretching modes of H 2O in the H 2O + Ar collision has been studied in a semiclassical method in the temperature range of 200–3000 K. The energy exchange probability increases slowly, but nearly linearly, with temperature over the entire range, reflecting a near-resonant case. The intermolecular removal of the energy mismatch (Δ E = + 105 cm −1) by translation is found to be nearly as efficient as the intermolecular transfer to the rotational motion. The energy exchange probability for D 2O + Ar is less efficiency by a factor of about two over the temperature range in both the intramolecular VR and intermolecular VT processes. The lower efficiency found in the VR step is due to a slower rotational motion of D 2O, while that in the VT process is due to a larger energy mismatch for the D 2O + Ar collision (Δ E = + 122 cm −1). The effect of molecular attraction is found to be important in the energy exchange process especially near room temperature, and the use of empirically determined attractive energies for the H 2O—Ar complex is found to be valuable at such temperatures.

Dependence of vibrational energy transfer and bond dissociation on initial excitation and phases in O2(0)+O2(v)

The dependence of vibrational energy transfer and bond dissociation on the initial vibrational energy and initial phases in the collision of two oxygen molecules O2(0)+O2(v) has been studied using classical trajectory procedures. When the initial vibrational energy of O2(v) is not large, the energy gained by O2(0) is mainly through the V→V pathway, but as the initial excitation increases the contribution of translational motion becomes important. For the highly excited O2(v), most trajectories lead to T→V energy transfer, and for such molecules dissociation probabilities are found to increase linearly with the initial excitation. The dissociation of O2(v) is sensitively dependent on the initial vibrational phase. For v=1, the resonant energy exchange probability is a linear function of the collision energy.

Vibrational energy exchange between an oxygen molecule and an adsorbed hydrogen atom

The dynamics of collision between an oxygen molecule and a hydrogen atom adsorbed on a metal surface has been studied. Time evolution of vibrational energies and bond vibrations has been studied in classical mechanics. The frequency difference between the colliding oscillators has been shown to vary with time during the collision, and the interaction system becomes temporarily a near-resonant case due to the collision-induced distortion. A semiclassical procedure has been developed to calculate VV energy exchange probabilities. We find that this procedure leads to a well-defined oscillatory probability representing an efficient VV energy exchange between the colliding oscillators. In addition, we find the formation of peroxyl radicals when there is a sufficiently strong attractive interaction between the collision partners.

Rotational and vibrational nonequilibrium effects in rarefied hypersonic flow

Results are reported for an investigation into the methods by which energy transfer is calculated in the Direct Simulation Monte Carlo method. Description is made of a recently developed energy exchange model that deals with the translational and rotational modes. A new model for simulating the transfer of energy between the translational and vibrational modes is also explained. This model allows the vibrational relaxation time to follow the temperature dependence predicted by the Landau-Teller theory at moderate temperatures. For temperatures in excess of about 8000K the vibrational model is extended to include an empirical result for the relaxation time. The effect of introducing these temperature dependent collision numbers into the DSMC technique is assessed by making calculations representative of the stagnation streamline of a hypersonic space vehicle. Both thermal and chemical nonequilibrium effects are included while the flow conditions have been chosen such that ionization and radiation may be neglected. The introduction of these new models is found to significantly affect the degree of thermal nonequilibrium observed in the flowfield. Larger, and more widely ranging, differences in the results obtained with the different energy exchange probabilities are found when a significant amount of internal energy is included in the calculation of chemical nonequilibrium.

Near-resonant vibrational energy exchange between the stretching levels of H 2O

The probabilities of vibrational energy exchange between the two stretching levels of H 2O have been calculated from 200 to 3000 K by use of a semiclassical procedure. Probabilities of the exothermic process (001 → 100) take a near-constant value of 0.35 over the entire temperature range, while the endothermic probabilities closely follow a 1/ T dependence. Probabilities exhibit a strong orientation dependence; large values are found when one of the H atoms is interacting with the incident atom in close proximity producing strong stretch-stretch couplings. Various intramolecular couplings during vibration are discussed. The effects of stretch-bend couplings and displacement of the O atom from the center-of-mass on the energy exchange is found to be unimportant.

Probabilities of vibrational energy exchange between carbon dioxide and carbon tetrafluoride

The deactivation rate constant of CO2(ν3) in mixtures with CF4 has been measured at 298 K. A pulsed CO2 laser was used to excite the CO2 molecules. To interpret the mechanism of energy exchange, the probabilities of V–V energy transfer for CO2–CF4 mixtures and the V-T self-relaxation of CF4(ν2) were calculated. The model used considers a Morse potential to describe the interaction between the molecules and the quantum mechanical first order distorted wave approximation to calculate the probabilities. Order of magnitude agreement between the experimental and calculated results for CO2–CF4 mixtures and for the CF4(ν2) self-relaxation is obtained.

Temperature dependence of the probabilities of VV energy exchange between H 2 and DCl

The temperature dependence of the removal of the vibrational energy of H 2 by DCl in H 2(1) + DCl(0) has been investigated over the range of 300–3000 K. The energy transfer probability of H 2(1) + DCl(0) → H 2(0) + DCl(1), where the vibrational energy of H 2(1) is removed by both the vibrational and rotational motions of DCl(0), is found to be strongly temperature dependent and increases with temperature closely following the relation log P α T 1/3. Over the temperature range it changes by two orders of magnitude. The probability of the near-resonant process H 2 (1) + DCl(O) → H 2(0) + DCl(2) is very close to that of the former at 300 K, but it increases only slightly as the temperature is raised to 3000 K. The sum of the probabilities of these two processes at 300 K is 3.4 × 10 −5, which agrees with the experimental value of 3.95 × 10 −5.

Vibration–vibration energy exchange in iodine molecules

Vibration–vibration energy exchange probabilities between iodine molecules (X 1Σ+g) have been calculated by use of the solution of the time-dependent Schrödinger equation. The interaction potential is constructed by summing four orientation averaged atom–atom interactions. One-quantum probabilities Pv,0v−1,1(T) for v−1,1→v,0 are found to be very large in a temperature range of 100–3000 K. At lower temperatures, the approximate linear relation pv,0v−1,1(T)≂vP1,00,1(T) holds. When v is small, the probability increases linearly with temperature. Multiquantum transitions v,0→v−n,n with n≳1 are found to be negligible near room temperature, but they become quite efficient at higher temperatures. Energy exchange probabilities are formulated in infinite order and their reduction to first-order expressions are discussed in detail. The effects of molecular attraction are also discussed.