Excitation Processes In Collisions Research Articles

Charge exchange, excitation, and ionization inH(1s)+He2+collisions simulated using the multichannel perturbed-stationary-state propagator

I recently reported [Phys. Rev. A 51, 2222 (1995)] on simulations of charge-exchange and excitation processes in collisions between a helium nucleus and a ground-state hydrogen atom that were performed in the multichannel perturbed-stationary-state framework without employing electron translation factors [Phys. Rev. A 51, 2199 (1995)]. A simulation with 45 adiabatic molecular orbitals reproduced the measured cross sections for electron capture and for the ensuing Lyman fluorescence lines of ${\mathrm{He}}^{+},$ up to the collisional ionization threshold $(\ensuremath{\sim}9\mathrm{k}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u}).$ In this study, the collision of ${\mathrm{He}}^{2+}$ on $\mathrm{H}(1s)$ is investigated further using a multichannel propagator defined over the former perturbed-stationary-state basis extended to include 35 ${L}^{2}$ ionization pseudostates of the linear combination of atomic orbitals (LCAO) type. The simulated total charge-transfer cross section is now in good agreement with experiment across the peak plateau and well into the falloff wing, where it begins to tail away at energies above 30 keV/amu because the LCAO ionization set is deficient. Concurrently, throughout the range where collisional ionization is important, state-selective cross sections are improved compared to our previous study. Approximately 25% of the calculated peak transfer cross section is associated with $n>~3{\mathrm{He}}^{+}$ levels. The multichannel propagator simulations imply that (i) decay cascades contribute almost one-third of the ensuing spontaneous He II Lyman-\ensuremath{\alpha} fluorescence cross section [J. Phys. B 24, 4025 (1991)] that is accurately reproduced and (ii) capture-induced Balmer-\ensuremath{\alpha} and Paschen-\ensuremath{\alpha} emissions are considerably stronger than the values either measured in the aforementioned experiment or computed by translation-factor models.

Interaction forces and energy transfer dynamics of LiH( 1gE +) and helium atoms II. Rotationally inelastic collisions and excitation efficiency

The weak, van der Waals interaction discussed in the preceding paper [9] for the ground electronic state potential energy surface of LiH( 1gE +) with He( 2gE) is employed in the calculation of rotationally inelastic state-to-state cross sections. Comparisons with the available experiments and with earlier calculations allow us to relate in detail the features of this anisotropic, short-range interaction potential with the outcomes of the collisional excitation processes. The corresponding excitation rates are also evaluated between the lower-lying rotational levels and for a range of temperatures of astrophysical interest.

Translational energy spectroscopy. Spin‐conservation studies in collisional excitation processes

AbstractHigh‐resolution translational energy spectroscopy is an effective means of obtaining detailed state‐selective information, permitting systematic investigation of spin conservation in collisional processes. In this paper, we examine collisional excitation of one selected singlet (N2) and one non‐singlet (O2) target by a variety of projectile ions, providing a kaleidoscope of assorted effects.

Ion-molecule processes in the interstellar medium. Rates for rotational excitations in NH 3-H + collisions

The collisional excitation of rotational states of NH 3 under the interaction with subthermal protons is studied via a sophhisticated, fully anisotropic potential function discussed before and by treating the multichannel scattering problem via the coupled-state (CS) approximation, It is found that one rotational level of NH 3 exhibits the largest probability to get collisionally excited and to be involved in postcollisional radiative emission at a specific frequency. The limited efficiency found for the multiple-jump collisional excitation processes also suggests that , at the temperatures of the interstellar medium, there should be a rather low concentration of rotationally “hot” NH 3 molecules.

Crossed molecular beams study of the M +( 1S)+Na(3 2S)→M +( 1S)+Na(3 2P) collision systems (M +=Li +, Na +, K +, Cs +) in the 0.05–3.00 keV energy range

An apparatus is described for the study of atomic electronic excitation processes in collisions between alkali ions and neutral alkali atoms. A thermal atom beam is crossed with an ion beam at energies varying from 0.05 to 3.00 keV and the fluorescence from the decay of excited atomic states formed by collision is measured (specifically in this paper the D-lines from Na(3 2P)). We report the apparatus construction, its calibration against previous data for the Li +Na system, total cross section data for Na +Na and K +Na for an energy range extended up to 3.00 keV, and new data for the Cs +Na system, which shows a broad maximum in the energy dependence of cross section between 1.50 and 2.00 keV.

A study of electron capture and excitation processes in collisions of multiply charged ions with lithium atoms

The atomic-orbital close-coupling method (AO-CC) has been employed in calculations of electron capture and target excitation in collisions of fully stripped ions Aq+ (q=2-6) with Li(ns,p) atoms (n=2,3) at low and intermediate energies. Total and state selective single electron capture (SEC) cross sections have been determined. Data for SEC into nl sub-levels of the projectile have been used to calculate the related line emission cross sections, which are compared with available experimental and theoretical data. In addition cross sections for various target excitation processes, in particular the Li(2s-2p) resonance transition are presented. The scaling properties of the total SEC and target excitation cross sections are investigated, and their implication for lithium beam edge plasma spectroscopy is being discussed. For completion, scaling relations for ionization are also given.

Excitation processes in collisions of inert gas ions with a Mg surface

Results of an angle resolved electron spectroscopy study of low keV inert gas ion collisions with a Mg surface are presented. Production of projectile autoionising states is demonstrated to exist not only for the previously known Ne case but also for He. The role of these states in ion production is commented. The characteristics of autoionising peak lineshapes are analysed and suggest a method of obtaining angular distributions of inelastically scattered ions.

Collisional excitation processes in reactive plasma

Collisional excitation processes in reactive plasma

HIGHLY CHARGED ION N6+ COLLISIONS WITH ATOM He INTO EXCITED STATES

The excitation processes in collisions between N6+ and He have been investigated by using the ECR ion source and the LHT-30 VUV Monochromator. The emission spectra shows that there are three channels of excitation in the N6+ and He collision system: (1) Single-electron capture into excited states. (2) Double-electron capture into excited states. (3) Direct excitation of indicident ions.

Effects of initial-state population variations on the 2p-->1s K alpha dielectronic satellite spectra of highly ionized iron ions in high-temperature astrophysical and laboratory plasmas.

Theoretical predictions are presented for the iron K\ensuremath{\alpha} x-ray emission spectra from high-temperature plasmas, assuming steady-state optically thin excitation conditions. Account has been taken of all fine-structure components of the 2p\ensuremath{\rightarrow}1s inner-shell-electron radiative transitions in the iron ions from Fe xviii to Fe xxiv. The K\ensuremath{\alpha} emission spectra are assumed to be produced by means of dielectronic recombination and inner-shell-electron collisional excitation processes that involve intermediate autoionizing states belonging to electronic configurations of the type 1${s}^{1}$2${s}^{r}$2${p}^{s}$. In addition to the electron-temperature variation, which is attributable to the temperature dependences of the radiationless electron capture and inner-shell-electron collisional excitation rate coefficients and to the temperature dependence of the charge-state distribution, the K\ensuremath{\alpha} emission spectra exhibit an electron-density sensitivity. This electron-density sensitivity is a result of the density-dependent distribution of populations among the different fine-structure levels of the initial ions in the dielec- tronic recombination and inner-shell electron collisional excitation processes.

New step impact electroluminescent devices

The step impact electroluminescent devices (SIED) and the multistep photon amplifier converted (SPAC) are proposed. The devices are a multilayered heterojunction structures in which the accelaration and collision excitation processes are spatially separated and permits independent optimization of each function in different materials. In collision excitation region, ballistic electrons excite the rare earth ions by direct impact. By changing conduction band step Δ E c we can tune up the energy of excited electrons to the resonance condition of a particular excited state of RE 3+ ions. The emission from the rare earth ions with transition wavelength shorter than semiconductor's band edge emission can be generated. The emission will contain narrow lines with gradual change in wavelength with temperature. The advantages of the new devices and excitation mechanism as discussed in detail. Laser action should also be obtainable by properly choosing device geometry. The laser oscillation at the rare earth transition assure the same wavelength from devices to devices with weak temperature dependence. The SIED structure is very promising structure for studying the direct impact excitation mechanism for a localized impurity in semiconductors. It can be used as a general tool for studying the excitation function of RE 3+ ions and other impurities with internal transitions like some transition metal impurities in III–V compounds.

A study of charge transfer and excitation processes in collisions of alpha particles with sodium atoms

The coupled state impact parameter model has been used to study collisions of alpha particles with sodium atoms. Straight-line trajectories are employed. The charge exchange and excitation cross sections are computed for impact energies in the range 10.0-270.0 keV. The calculated total charge exchange cross sections are found to be in good agreement with the recent experimental data of Dubois and Toburen (1985) in the energy range 10.0<or=Elab<or=100.0 keV. It is predicted that above this energy electron capture from the L shell starts to compete with electron capture from the M shell which is considered. The authors find that, for impact energies below 30.0 keV, the electrons are preferentially captured in the He+ (3l) state. This leads to a distinct possibility of population inversion and emission of Lyman- alpha (304 AA) and Lyman- beta (256 AA) soft X-ray photons.

A method of excitation profiling in high-field electroluminescence

A method of quasidirect profiling of impact excitation of electroluminescence in a metal semiconductor junction utilizing the Auger quenching of a localized center luminescence by either free or weakly bound electrons is described. Experimental results obtained on CdF2:Mn,Y Schottky diodes unambiguously prove a spatial separation of the acceleration and collision excitation processes in high-field electroluminescence.

Where the metal-semiconductor junction emits light

Determination of the spatial distribution of excited luminescence centers in a junction is crucial for testing any model of high-field electroluminescence. A simple method of a quasi-direct profiling of emission in a metal-semiconductor (MS) junction is introduced. The method is based upon the effect of Auger quencing of a localized-centre luminescence by either free or bound electrons. Since the efficiency of this effect is controlled by the Fermi-level position the kinetics of electroluminescence (EL) is governed by the motion of a depletion layer edge following a rapid change of a junction bias. Simultaneous measurement of the EL kinetics and width of a depletion layer allows for a determination of a spatial excitation profile. The method is illustrated by the experiment performed on EL-MS diodes made on CdF 2:Mn, Y crystals. It is shown that EL is generated only in a region close to the depletion layer edge, thus proving a spatial separation of the carrier acceleration and the collision excitation processes in high-field electroluminescence.

Theoretical study of Ne-Ne collisions

The molecular framework of Ne-Ne collisional excitation processes in the moderate energy range is reported. Diabatic-like orbitals, fulfilling the diabatic correlations of Lichten (1967) are calculated in two different approximations termed frozen-orbital and rotated-orbital methods. The coupling terms and potential energies computed in both approximations show that the excitation mechanism proposed by Brenot et al. (1975) is not consistent with the experimental findings. Quantal differential cross section calculations performed in the frozen-orbital and in the rotated-orbital approximations show the consistency of these two diabatic approaches. These calculations also show that the excitation processes are primarily induced at the crossings between the promoted 4f sigma u molecular orbital and empty Rydberg sigma u molecular orbitals. The investigation of secondary mechanisms following the sigma u sigma u primary transitions demonstrates that the one- and two-electron processes favour the Ne(2p53p) levels.

Chemical Applications of Metastable Argon Atoms. III. Production of Krypton and Xenon Metastable Atoms

An inexpensive experimental technique has been developed for the production of argon, krypton, and xenon metastable atoms using a discharge-flow system. The reactions of these metastable atoms with N2, CO, and N2O were investigated in the pressure range 0.3–10 torr, and the emission spectra resulting from the reactions were identified. These spectra gave information about the collision event and also about some of the relaxation processes. Franck–Condon factors apparently do not control the molecular excitation processes in collisions of excited heavy atoms with light diatomic molecules. This discharge flow source of metastable atoms provides emission spectra of sufficient intensity from added CO and N2O for study of emission bands which currently are not well understood. Molecular emission from N2O has been observed, apparently for the first time.