Mean Collisional Energy Research Articles

Pulse Radiolysis Studies of Collisional Deexcitation of Ne(3P1) by H2

The cross sections for the deexcitation of Ne(3P1) by H2 have been measured as a function of the mean collisional energy in the range of 17.3-37.9 meV or in the temperature range from 134 K to 293 K using a pulse radiolysis method as combined with time-resolved optical absorption spectroscopy. The deexcitation cross sections are in the range of 2.1- 5.6 Å2 for Ne(3P1) and nearly constant or increase slightly with increasing the collisional energy.Journal of Institute of Science and Technology, 2014, 19(1): 75-78

Collisional energy loss of heavy quarks

We develop a transport approach for heavy quarks in a quark-gluon plasma, which is based on improved binary collision rates taking into account quantum statistics, the running of the QCD coupling and an effective screening mass adjusted to hard-thermal loop calculations. We quantify the effects of in-medium collisions by calculating the heavy flavor nuclear modification factor and the elliptic flow for RHIC energies, which are comparable to radiative effects. We also derive an analytic formula for the mean collisional energy loss of an energetic heavy quark in a streaming quark gluon plasma.

Collisional deexcitation of the excited rare gas atoms in resonant states: The Watanabe–Katsuura theory revisited

The cross sections for the collisional deexcitation of neon atoms in the lowest excited P11 state by Ar, Kr, Xe, N2, O2, CO, NO, and CH4, and in the lowest excited P13 state by O2 and CH4 have been measured at a mean collisional energy corresponding to room temperature. Data are also included for collisions of argon atoms in the lowest excited P11 and P13 states by C2H4, cyclo-C3H6, and C3H8, and collisions of krypton atoms in the lowest excited P11 and P13 states by C2H4 and cyclo-C3H6. The measured cross sections, together with those obtained in our previous studies, are compared with the cross sections calculated using the Watanabe–Katsuura theory. An extension of the Watanabe–Katsuura theory to the deexcitation of excited rare gas atoms in collisions with molecular quenchers, not atoms, is examined.

Deexcitation of Ne(3P1) and Ne(3P2) in collisions with Ar, Kr, and Xe

The cross sections for the deexcitation of Ne(3P1) and Ne(3P2) by Ar, Kr, and Xe have been measured as a function of the mean collisional energy in the range of 17–38 meV or in the temperature range from 133 K to 295 K using a pulse radiolysis method combined with time-resolved optical absorption spectroscopy. The deexcitation cross sections are in the range of 18–26 Å2 and 11–20 Å2 for Ne(3P1) and Ne(3P2), respectively, and increase slightly with increasing the collisional energy. The absolute experimental cross sections for the Ne(3P1) deexcitation are in relatively good agreement with the total Penning ionization cross sections obtained by an optical model calculation, which shows the importance of an electron-exchange interaction in the deexcitation of Ne(3P1) in collisions with Ar, Kr, and Xe. The absolute cross section values for the deexcitation of resonant Ne(3P1), which are only slightly larger than those for the deexcitation of metastable Ne(3P2), have also supported the discussion on the deexcitation mechanism of Ne(3P1) by Ar, Kr, and Xe.

Deexcitation of He(2 1P) in a collision with Ne

Collisional deexcitation cross sections of He(2 1P) by Ne have been measured in a region of the mean collisional energy between 17 and 38 meV using a pulse-radiolysis method. Measured cross sections are in a range of 20–25 Å2 and increase with increasing collisional energy. The experimental cross sections are compared with the calculated ones for total and partial excitation transfer into highly excited Ne atoms. Fairly good agreement between calculated and experimental results indicates that in the deexcitation of He(2 1P) the excitation transfer into Ne*(6p3, 5s2, or 6s4) is important in the measured mean collisional energy region. It is also shown that a dipole–dipole interaction plays an important role in the excitation transfer from He(2 1P) to Ne.

Deexcitation cross sections of Ne(3P2, 3P1, and 3P) by molecules containing group-IV elements

Deexcitation cross sections of Ne(3P2), Ne(3P1), and Ne(3P0) by CH4, SiH4, GeH4, CF4, and SiF4 have been measured at a mean collisional energy corresponding to room temperature (295 K) and compared systematically with those by other molecules to understand general features of the cross section values dependent on both the electronic states of excited neon atoms and the target molecules. A small difference in the cross section values between metastable atoms, Ne(3P2) and Ne(3P0), and a resonant atom, Ne(3P1), has indicated that Penning ionization by Ne(3P1) is mainly governed by an electron exchange interaction rather than a dipole–dipole interaction. A spatial electron distribution of the outermost orbital of a target molecule is especially of great importance in the determination of the absolute cross section values in the deexcitation of excited neon atoms due to an electron exchange interaction.

Deexcitation cross sections of He (2 3S, 2 1S, and 2 1P) by molecules containing group-IV elements

Deexcitation cross sections of He(2 3S), He(2 1S), and He(2 1P) by C2H6, Si2H6, CF4, SiF4, and SiCl4 have been measured at a mean collisional energy corresponding to room temperature (295 K) and compared systematically with those by CH4, SiH4, and GeH4 (previously reported) to understand general features of the cross section values dependent on both the electronic states of excited helium atoms and the target molecules containing group-IV elements and to substantiate further the deexcitation mechanism. In the de-excitation of the metastable atoms, He(2 3S) and He(2 1S), the magnitude of the cross sections has mainly been ascribed to a short-range electron exchange interaction. The obtained cross section values for He(2 3S) are compared with a semiempirical formula and it is concluded that the number of the equivalent electrons which can be ionized with the excitation energy of He(2 3S) and the lowest ionization potential of the target molecule are of great importance in determination of the cross section values. Systematic comparisons of the deexcitation cross section values of the resonant atom, He(2 1P), with theoretical ones have shown an importance of not only deexcitation transition mainly ascribed to a long-range dipole–dipole interaction between He(2 1P) and a target molecule but also a bent trajectory caused by an attractive interaction potential between them to determine the cross section values.

Deexcitation of He(2 1P) in collisions with diatomic molecules

Deexcitation cross sections of He(2 1P) by N2 and O2 have been measured using a pulse radiolysis method in a region of the mean collisional energy between 18 and 38 meV. Fairly large deexcitation cross sections (≂100 Å2) by N2 and the negative slope of the curve of cross section vs energy are interpreted in terms of the energy transfer cross section based on a dipole–dipole interaction. Validity of theoretical formula based on a semiclassical approach with rectilinear trajectories, i.e., the Watanabe–Katsuura formula, is discussed. The deexcitation cross section of He(2 1P) by O2 and its collisional energy dependence are not very different from that by N2. Optical model calculation of the deexcitation cross section has been also presented for collisions between He(2 1P) and M (M=H2 or N2) with an isotropically averaged complex potential optimized through a fitting procedure to the experimental cross sections. It has been found by the model calculation that an electron exchange interaction is not negligible in the deexcitation process.

Deexcitation of He(2 1P) in a collision with a hydrogen molecule

Deexcitation cross sections of He(2 1P) by H2 have been measured using a pulse radiolysis method in a region of the mean collisional energy between 18 and 38 meV and compared with those obtained by theoretical calculations. Experimental cross-section values and their collisional energy dependence are interpreted in terms of the Penning ionization cross section based on a long-range dipole–dipole interaction between He(2 1P) and H2. Validity of the theoretical formula for the Penning ionization cross section, i. e., the Watanabe–Katsuura formula, is discussed. The cross section has been further calculated by means of an impact-parameter method with experimentally simulated classical trajectories; a hydrogen molecule has been assumed to be spherical to neglect the rotational effect of H2; it is also assumed that the polarization axis of the p-state helium rotates in order to keep collinear or perpendicular configuration with respect to the axis of He–H2. A modified form of the dipole–dipole autoionization width with an electron exchange interaction is also discussed.

Deexcitation of He(2 1P) in collisions with rare gas atoms

Deexcitation (Penning ionization) cross sections of He(2 1P) by Kr and Xe have been obtained in a region of mean collisional energy between 18–38 meV by a pulse radiolysis method. Fairly large cross sections of above 100 Å2 and their collisional energy dependence are interpreted by the Penning ionization cross sections based on a long-range dipole–dipole interaction. Validity of the theoretical formula for the Penning ionization cross section (the Watanabe–Katsuura formula) is discussed. Two kinds of the cross sections have been further calculated by means of the impact parameter method with experimentally simulated classical trajectories; in one procedure, the polarization axis of the p-state helium has been assumed to rotate in order to keep collinear or perpendicular configuration with respect to the interatomic axis, in the other procedure, the polarization axis is fixed in a certain direction. The classical motion of the particles have been shown to cause considerable influence on the absolute values and the collisional energy dependence of the cross sections. The influence has increased accordingly to the attractive force of the interatomic potential, i.e., in order of Ar<Kr<Xe. Modified form of the dipole–dipole autoionization width with the electron exchange interaction is also discussed. It has also been suggested that rotation of the p-state atomic polarization depends strongly on the van der Waals interaction with the target atoms. The effect of the rotation has been shown to be most prominent for Xe but small for Ar.

Deexcitation cross sections of He(2 1P) by atoms and molecules

The deexcitation cross sections of He(2 1P) by M (M=Kr, Xe, H2, D2, N2, CO, O2, NO, CO2, and CH4) have been obtained by a pulse radiolysis method at a mean collisional energy corresponding to room temperature. The cross sections have been explained fairly well by the Penning ionization process with a long-range dipole–dipole interaction. Bent trajectories appear to be important in the deexcitation by spherical atoms and molecules. An electron exchange process is also suggested to give an important contribution to the total decay width of the transient collision complex in highly excited autoionizing states of (HeM)*.

Collisional perturbation of regular and irregular intramolecular dynamics: A model quantum-mechanical study

A quantum-mechanical study is presented of energy transfer in collinear atom-molecule inelastic collisions. The molecular potential is the well studied two-mode, Henon-Heiles potential. Two atom-molecule interaction potentials are considered: a weak exponential repulsive potential (previously considered in a classical study by Schatz), and a Morse attractive interaction. For these two potentials, the mean energy transfer and transition probabilities, classified according to the “category of chaos” (normal-mode, local-mode, or mixed-mode states), are compared, as functions of the total energy. The classical critical energy for the molecular potential plays no role in the energy dependence of the mean collisional energy transfer. In addition, preservation of memory (hysteresis) about the initial category of chaos is larger for collisions involving the weak repulsive potential.

Deexcitation Probabilities of Ne(<sup>3</sup>P</sub>2</sub>) by Xe for the Case E << D

The deexcitaion probability calculation of the total Penning ionization cross sectionfor Ne(3P2) by Xe has been made in the region of the collisional energy from 18.5 to 38.1meV. The experimental cross sections have been compared with the deexcitation probabilityfor Ne(3P2) by Xe. Considering the magnitude of the mean collisional energy with respect toD, the application of the analysis in the case E >> D is expected to be more appropriatethan in the case E << D. For further insight into this results, it is also of great importanceto evaluate theoretical investigations of Ne(3P2) by Xe for the case E >> D.Keywords: Metastable atoms, deexcitation probabilities, pulse radiolysis, collisionalenergy, potential well depthDOI: 10.3126/jncs.v25i0.3304Journal of Nepal Chemical Society Volume 25, 2010 pp 70-74

Deexcitation Probabilities of Ne(<sup>3</sup>P<sub>2</sub>) by Kr for the Case E << D

The deexcitation probability calculation of the total Penning ionization cross section for Ne(3P2) by Kr has been made in the region of the collisional energy from 18.5 to 38.1 meV. Considering the magnitude of the mean collisional energy with respect to D, the application of the analysis in the case E >> D is expected to be more appropriate than in the case E << D. Theoretical investigations of Ne(3P2) by Kr for the case E >> D are also needed.Keywords: metastable atoms, resonance atoms, deexcitation cross sections, pulse radiolysis, impact parameter.DOI: 10.3126/jncs.v24i0.2390Journal of Nepal Chemical Society Vol.24 Page 45-48

Deexcitation Probabilities of Ne(3P2) by Ar for the Case E << D

The deexcitaion probability calculation of the total Penning ionization cross section for Ne(3P2) by Ar has been made in the region of the collisional energy from 18.5 to 38.1 meV. Comparing the magnitude of the mean collisional energy with respect to D, the application of the analysis in the case E >> D is expected to be more appropriate than in the case E << D. More advance theoretical investigations for Ne(3P2) by Ar should consider the further understanding. Keywords: Deexcitation cross section; Collisional energy; Pulse radiolysis method; Metastable atoms; Impact parameter.DOI: 10.3126/jncs.v24i0.2382 Journal of Nepal Chemical Society, Vol. 24, 2009 Page: 19-23