Energy Transfer Cross Sections Research Articles

Rotational energy transfer in HF–Li collisions

We report state-to-state integral inelastic cross sections for rotational energy transfer in rigid rotor HF–Li collisions, at a relative translational energy of 8.7 kcal mol−1. The results have been analyzed in terms of power gap law, information theoretic synthesis using energy and angular momentum constraints, and energy corrected sudden and energy corrected sudden-power law scaling relations.

Rotational energy transfer cross sections in methane ( 13CD 4) from infrared double resonance measurements

Rotational relaxation times have been measured for methane ( 13CD 4) in collisions with itself, He, Ne, Ar, Kr, Xe, and CH 2F 2, using the method of infrared double resonance. Collision efficiencies range from one-half to greater than gas-kinetic, and the measured relaxation times are longer in the vibrational ground state than in the υ 4 = 1 excited state.

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.

New interpretation of spin-wave behavior in nickel.

Results from recent calculations of the neutron-scattering cross section for energy transfer up to 1 eV have led to a new picture of spin waves in nickel, one in which spin waves exist out to the zone boundary. Our prediction of the dispersion curve and peak widths is in general agreement with data from subsequent neutron-scattering experiments. This provides additional evidence that the ''average'' spin-splitting energy for nickel is in the 300- to 400-meV range.

A molecular beam study of electronic to electronic, vibrational, and rotational energy transfer in the collision of two step laser excited sodium with N2

The quenching of excited Na* (4d,5s,4p,4s) by N2 has been studied in a crossed atomic and molecular beam apparatus at thermal collision energies. The sodium atoms are excited by two laser beams of different wavelengths to either the 42D5/2 or 52S1/2 state, via the intermediate 32P3/2 state. For both excitation schemes optical relaxation processes lead to a population in the 42P3/2 and 42S1/2 states of several percent. The relative densities of the excited states have been calculated from rate equations using stationary conditions. The measured energy transfer spectra show high scattering intensities at low kinetic energies together with some structure at medium energies. This structure can be partially disentangled using the results of the previously studied Na*(32P3/2)+N2 quenching process. The main conclusion is that collisional deexcitation to the Na(3s) ground state is negligible, whereas among the higher levels the collisional energy transfer cross sections are between 0.5 and 7.5 times the magnitude of the 3p–3s quenching cross section and they are strongly forward peaked in the same way. Relative values for the differential quenching cross sections are reported.

The characteristic energy and momentum transfer cross section for low-energy electrons in neon

The characteristic energy of low-energy electrons in neon gas has been measured at room temperature by the Townsend method as a function of the reduced electric field, E/N, where E denotes the field strength and N the number density of the gas atoms. The measured characteristic energy was 0.127 eV at E/N=0.014 Td and increased monotonously with increasing E/N. The momentum transfer cross section for electrons in neon was derived from the data for an energy range from 0.01 to 1 eV. The result was found to be in excellent agreement with previous estimates obtained by different methods, particularly for the energy range from 0.1 to 0.5 eV. All of the four theoretical cross sections calculated by Thompson, Garbaty and LaBahn (1971), Yau et al (1978) and McEachran and Stauffer (1978) agree with the authors' experimental cross section within about +or-20%.

Collisional energy transfer in the low-pressure-limit unimolecular dissociation of HO2

Classical trajectory calculations are used to investigate the energy transfer properties of HO2–He collisions under conditions where HO2 is initially excited to energies near dissociation. The emphasis in this investigation is on determining the dependence of vibrational energy transfer characteristics on heat bath temperature, total molecular energy, and total molecular angular momentum. Vibrational energy transfer is a function of all three variables. Energy transfer averages, correlation coefficients, and energy transfer cross sections are used to determine the energy transfer mechanism. Evidence is found for all types of energy transfer, but the specific mechanism for a particular ensemble is highly dependent on the initial variables. At fixed vibrational energy and heat bath temperature, the magnitude of the average vibrational energy transferred per collision ‖〈ΔE′〉‖ increases with increasing molecular angular momentum. At fixed initial molecular angular momentum and heat bath temperature, −〈ΔE′〉 increases as the total energy in the molecule increases, except for very low values of initial angular momentum. Increasing the heat bath temperature for fixed values of the other initial variables decreases the magnitude of 〈ΔE′〉. The relative importance of weak and strong collisions in governing the energy transfer characteristics is discussed. In particular, the probability density function for vibrational energy transfer is not well represented by a simple ‘‘exponential down’’ model. A double exponential function is required to represent the long tail of the distribution adequately. Total vibrational energy transer cross sections determined from vibrational energy transfer histograms are weak functions of total energy, total angular momentum, and heat bath temperature. They are systematically higher than the corresponding Lennard-Jones cross sections.

A new rigid-rotor H2–CO potential energy surface from accurate a b i n i t i o calculations and rotationally inelastic scattering data

We determined a new rigid-rotor potential energy surface for H2–CO by combining large basis set SCF calculations with damped long range dispersion coefficients. The damping function contains two parameters which were determined by comparison of experimental and calculated cross sections for oD2–CO scattering at E=87.2 meV. The dynamical calculations were performed within the coupled states approximation because neither a classical nor an energy sudden description of the CO rotation are accurate enough. It is found that the rotational rainbow structures of the energy transfer cross sections determine the relative anisotropy of the interaction potential, while the diffraction oscillations of the total differential cross section determine the absolute range of the effective spherically averaged potential. For a unique potential determination both sets of experimental data have to be fitted simultaneously.

Differential cross sections for (R,T) energy transfer in He–HF collisions: Comparing theory with experiments

Starting from a recently proposed potential energy surface, the relative occurrence of rotational inelasticity during He–HF collisions at thermal energies is examined as a function of scattering angle by employing both rigorous ab initio calculations (CC) and approximate solutions of the scattering equations (IOSA). The chosen range of energy is the same as one recently studied in highly accurate molecular beam experiments, so that rather close scrutiny of the computational outcome is made possible by comparison with measured differential cross sections (DCS) over a wide angular region well beyond the rainbow angle. The possible effect of isotopic substitution and the reliability of energy sudden schemes are investigated by computing both total and individual DCS involving rotational transitions. A very satisfactory fit to the measured total DCS is found within the IOSA approximation, thus providing further checks on the quality level of the employed potential surface. The general inefficiency in this system of energy deposition into rotations at thermal collision energies is here indicated by both theory and experiments.

Cross sections for collisional energy transfer between low-lying electronic states of magnesium oxide (X1.SIGMA.+, a3.PI., A1.PI.) in collisions with nitrous oxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCross sections for collisional energy transfer between low-lying electronic states of magnesium oxide (X1.SIGMA.+, a3.PI., A1.PI.) in collisions with nitrous oxideBrigitte Pouilly, Jean Michel Robbe, and Millard H. AlexanderCite this: J. Phys. Chem. 1984, 88, 1, 140–148Publication Date (Print):January 1, 1984Publication History Published online1 May 2002Published inissue 1 January 1984https://doi.org/10.1021/j150645a033RIGHTS & PERMISSIONSArticle Views46Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Classical collisions of protons with hydrogen atoms

High speed storage required: 47 kwords (modifications are deNature ofphysicalproblem scribedwhich reduce the storage to 38 kw.) The program solves the equations of motion for the interaction of 3 charged particles, obtaining final states in termsof No. of bits in a word: 60 initial states, and energy transfers, anglesof ejection, and final cartesian co-ordinates of relative motion. Using aMonte Carlo method on many orbits total ionization and charge transfer * Present address: Operations Research Unit, AERE Harwell, cross sections, integral energy transfer cross sections and moOxfordshire OX1 1 ORA, U.K. ments of energy transfers are estimated. Facilities are provided

Vibrational-rotational energy transfer in collisions of HF (v=4, J=20) with rare gases

State-to-state energy transfer cross sections for He and Ne+HF(v=4, J=20) at 0.2 eV initial relative translational energy were computed using quasiclassical trajectories. These results are compared with previously published results for Ar+HF at the same initial conditions. The results show that the number of final J states populated in a given final v state increases and that the magnitudes of the state-to-state cross sections decreases as the size of the rare gas atom decreases. The cross sections for vibrational transitions are not sensitive to the size of the rare gas atom.

Cross sections for energy transfer in collisions between two excited sodium atoms

We have measured cross sections, ${\ensuremath{\sigma}}_{\mathrm{nL}}$, for the excitation transfer process $\mathrm{Na}(3P)+\mathrm{Na}(3P)\ensuremath{\rightarrow}\mathrm{Na}(3S)+\mathrm{Na}(\mathrm{nL})$, where $\mathrm{nL}$ is the $4D$ or $5S$ level. Our results are ${\ensuremath{\sigma}}_{4D}=23 {\AA{}}^{2}\ifmmode\pm\else\textpm\fi{}35%$ and ${\ensuremath{\sigma}}_{5S}=16 {\AA{}}^{2}\ifmmode\pm\else\textpm\fi{}35%$ at $T\ensuremath{\sim}600$ K. To obtain these cross sections we have used pulsed excitation and measured the intensities of $4D$, $5S$, and $3P$ fluorescence emissions, and the spatial distribution of excited atoms resulting from radiation diffusion, as well as the excited atom density as a function of time. Additionally, we have accounted for (time-dependent) radiation trapping of $3P$ and $\mathrm{nL}$ level radiation and for the resulting anisotropies of these fluorescence emissions. Comparisons of our results with theory have been made, and their relevance to other experiments is discussed.

Rotational energy transfer in collisions of internally excited molecules. Effect of initial conditions and potential energy surface

We report quasiclassical trajectory calculations for the effect of potential energy surface, initial vibrational state, and initial translational energy on cross sections for rotational energy transfer in nonreactive collisions. We also study whether the effect of initial vibrational excitation is different for systems that allow reaction from those that do not. The systems studied are Ar+HF, Ar+H2, and H(D)+H2 on a total of five potential energy surfaces. The most important trend is that if rotational-translational energy-transfer cross sections are small (<4a20) for the ground vibrational state, then they increase markedly upon vibrational excitation; but if they are large (20–110a20) for the ground vibrational state, then they change very little. We present tables of the state-to-state rotational energy cross sections to illustrate finer details of the trends.

Quasiclassical trajectory state-to-state cross sections for energy transfer in Ar+ OH(υ = 9, J = 0,4, and 8) collisions

State-to-state energy transfer cross sections have been computed for Ar + OH(υ 1 = 9; J i = 0,4, and 8) at initial relative translational energy 0.2 eV using quasiclassical trajectories. The results show that a relatively small amount of initial rotational excitation has a significant effect on the energy transfer. The energy transfer for J i = 8 is dominated by transitions for which the vibrational and rotational energy changes are such that the translational energy changes are minimized.

Interaction potentials and energy transfer cross sections for collisions of metastable helium and neon. II. He(21S)+Ne

Differential cross sections for elastic and excitation transfer scattering were measured for He(21S)+Ne collisions at kinetic energies between 25 and 225 meV. A kinematic analysis and time-of-flight measurements show that Ne atoms can be excited into all energetically allowed states. From simultaneous fits of the elastic and inelastic differential cross sections information is obtained on the interaction potentials and the energy transfer cross sections. Total cross sections are in agreement with measurements in He-Ne discharges. The threshold for the pumping process of the 6328 AA line of the He-Ne laser, He(21S)+Ne to He+Ne(2p55s 1P1), is higher than previously assumed. The potential curves derived offer a simple explanation of the large differences in the cross sections for He(21S)+Ne to He+Ne(2p55s1P1 and 3P0,1,2), which is inconsistent with the commonly accepted Wigner spin rule.

A Monte Carlo quasiclassical trajectory study of energy transfer in Ar+HF collisions

Quasiclassical trajectories on a pairwise-additive potential-energy surface have been used to compute state-to-state cross sections for energy transfer in Ar+HF. Interest is focused upon relaxation from high vibration-rotation states. Pure-rotational energy transfer in excited vibrational states, vibrational relaxation, and the effect of relative translational energy on the energy transfer were also investigated. Most of the calculations were carried out for 1.0 eV relative translational energy. Initial vibrational states vi = 0, 2, 4, and 6 and initial rotational states Ji = 0, 10, 20, 30, and 40 were studied at this collision energy. The energy transfer for initial state vi = 4, Ji = 20 was studied at the initial relative translational energies 0.2, 0.4, 0.6, 0.8, and 1.0 eV. For collisions of Ar with highly excited HF the dominant energy transfer is V-R. The energy transfer results in an increase in the rotational state for downward vibrational transitions and a decrease in rotational state for upward vibrational transitions. The results suggest that pure-rotational energy transfer for low levels of rotational energy (Ji≲10), even in high vibrational states, should be accurately described by the rigid-rotor approximation. None of the energy transfer processes has a strong dependence on the initial relative translation energy, however, the influence is not negligible in all cases.

Laser induced fluorescence study of first part of a Na/Na 2 free jet expansion: dimer formation and excitation-energy transfer

The very first part of a Na/Na 2 free jet expansion (0 to 1.5 nozzle diameters, D is studied by means of laser induced fluorescence. Fluorescence intensifies originating from various (υ, J) states of the Na 2 molecules are measured as functions of the distance y from the orifice along the axis of the expansion. By means of these measurements the evolution of the total number of dimers in the course of the expansion is studied. This is done for expansions with stagnation conditions ranging from p oD = 0.5 to 10 Torr mm. From the dependence of the results on p o we find that for the highest densities a radiation quenching mechanism becomes important for the interpretation of the data. It consists of a collisional transfer of the electronic excitation energy from the dimer to an atom, followed by the trapping of the subsequent atom radiation. For the energy transfer cross section we obtain a value of 80 ± 20 A 2. About the dimer formation we find that throughout the expansion the relative increase of the number of dimers is proportional to p oD . The major part of the dimerisation occurs just outside nozzle in the region 0–0.7 D. The dependence of the formation on y can be described by a universal function ϕ( y) for which an empirical form is deduced from the data. The total net increase in dimer mole fraction is found to be 4.5%/Torr mm.

Interaction potentials and energy transfer cross sections for collisions of metastable helium and neon I: He(23 S)+Ne

Differential cross sections have been measured for He(23 S)+Ne at kinetic energies between 28 and 370 meV. For energies above 90meV the elastic cross sections show Stuckelberg oscillations from curve crossings, which lead to the energy exchange process: He(23 S)+Ne→He(11 S)+Ne(2p 5 4s,3d,4p). Differential cross sections for this inelastic process could be measured above 200 meV. A fit to the data gives the potentials for He(23 S)+Ne and, less accurately, for He+Ne*. These results offer a simple explanation, why the exothermic pumping process of the infrared lines of the HeNe laser has a threshold of about 80 meV and a small cross section.

Vibrational and rotational energy transfer in Ar + HF

State-to-state energy transfer cross sections for Ar + HF ( v = 2, 4, and 6; J = 4, 6, 8, and 10) were computed using quasiclassical trajectories. Rotational energy transfer is invariant with increasing v, but vibrational energy transfer is significantly enhanced by increasing J.