Inelastic collisions of electrons with atoms in an electric field

Formulas have been obtained in the Bethe—Born approximation for the excitation cross section of atoms by electrons in a constant electric field. The influence of the electric field is reduced to the accumulation of momentum by the incident electron and the variation of the electronic configuration of the atom. The collision cross section is in the form of two components d and d_¦, which correspond to collisions with transfers of the momentum components to the perpendicular and parallel electric field. The angular dependence of the cross section is determined by the anisotropy coefficients _tT and_¦. In the general case these coefficients depend on the polar and azimuthal angles and .Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 10–13, September, 1989.     

Method of determining absolute cross sections of collisions of the second kind between Hg(63P0,2) atoms and slow electrons

An equation giving the absolute cross sections q₂₁(u) of collisions of the second kind between excited atoms and slow electrons is obtained. The determination of q₂₁(u) entails measurement of the current on the collector which is due to collisions of the second kind and the effective life of the investigated level. The value of q₂₁(u) and Hg(6³P_0,2) was calculated. The value of q₂₁(u) was determined for the following slow-electron energies: in the case of Hg(6³P₀) q₂₁(u)=2.6 · 10^–15 cm² for u=0.13 eV and for Hg(6³P₂) q₂₁(u)=1.1 · 10^–15 cm² for u=0.3 eV. The obtained results are compared with other experimental and theoretical data and are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika No. 2, pp. 42–45, February 1975.     

Relativistic calculations of inelastic collisions between electrons and atoms

The Feynman S-matrix formalism is used to consider the inelastic collisions of electrons with a hydrogen atom. The two leading Feynman diagrams are calculated, and the 1s-2s transition is treated in detail. Results are given for scattering amplitudes at energies of 1.0–8.0 (atomic units) and for various scattering angles, as well as the differential cross sections for direct scattering in the energy region 1.36–118.5 keV. On the basis of comparison with nonrelativistic calculations, we conclude that relativistic effects are appreciable and increase with energy. Total cross sections are calculated in both nonrelativistic and relativistic approximations. The difference between them increases with energy and is 15–20% for energies of 20–50 keV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 7–12, August, 1977.     

Inelastic electron collisions with Rydberg atoms

The standard classical method of computer simulation is used for evaluation of the inelastic cross section in electron collisions with a highly excited (Rydberg) atom. In the course of collision, the incident and bound electrons move along classical trajectories in the Coulomb field of the nucleus, and the scattering parameters are averaged over many initial conditions. The reduced ionization cross section of a Rydberg atom by electron impact approximately corresponds to that of atoms in the ground states with valence s-electrons and coincides with the results of the previous Monte Carlo calculations. The cross section of an atom transition between Rydberg atom states as a result of electron impact is used for finding the stepwise ionization rate constant of atoms in collisions with electrons or the rate constant of three-body electron-ion recombination in a dense ionized gas because these processes are determined by kinetics of highly excited atom states. Surprisingly, the low-temperature limit of electron temperatures is realized when the electron thermal energy is lower than the atom ionization potential by about three orders of magnitude, as follows from the kinetics of excited atom states. The article is published in the original.     

Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient β on the excited state ( 2³ P ₂) and metastable state ( 2³ S ₁) populations is also investigated. From these results we infer a rather uniform rate constant K _sp = (1±0.4)×10^-7 cm³/s. Received 8 September 2000 and Received in final form 19 December 2000     

Frequency of collisions between electrons and gas and vapor atoms and molecules

A resonant method based on the phenomenon of electron cyclotron resonance is used to determine the frequency of collisions between electrons and He, Ar atoms and H₂S, SO₂, H₂O, and CsCl molecules. Electron distribution over energy is measured under experimental conditions and the mean electron energy determined therefrom. Existing techniques of collision frequency measurement and calculation are discussed. Experimental dependences of reduced collision frequency on mean electron energy are obtained and the parameter E/N is compared to values presented in the literature.     

Inelastic scattering of fast electrons from metastable states of helium

Inelastic scattering cross sections for collisions of electrons with helium atoms in metastable 2 ^1,3 S states are calculated for some final states of S and P symmetry by using the First Born Approximation and the Random Phase Approximation. The results for the total cross sections compare reasonably well with previous accurate values in the case of singlet-singlet transitions.     

Energy pooling to the level arising from collisions between pairs of metastable atoms

The energy-pooling rate coefficient for the process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination line and the metastable atoms in the 6s5d state were produced due to radiative and collisional depopulation of the laser-excited 6s6p state. The measurements were performed at number densities of about and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to the trip let metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line 791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single mode ring dye laser. The rate coefficient was found to be at . Received: 11 April 1997 / Revised: 24 September 1997 / Accepted: 10 December 1997     

Inelastic collisions of slow electrons with yttrium trichloride molecules

Inelastic collisions of electrons with YCl₃ molecules are investigated by the method of extended crossing beams. As in the case of LaCl₃ molecules, only the spectral lines of singly charged metal ions are found, with the lines of yttrium atoms and the spectral bands of yttrium monochloride being absent. The excitation cross sections of the energy levels of Y(II) and the contribution of the cascade population are calculated using the results obtained. Possible reaction channels upon dissociative excitation are discussed.     

Observation of multichannel collisions of cold metastable calcium atoms

Recent theoretical work indicates that collisions between metastable alkaline-earth atoms (AEAs) in the presence of external magnetic fields should be largely determined by partial waves with large angular momenta even at very low temperatures. Unusually large inelastic collision cross sections were predicted and doubts have been raised regarding the feasibility of evaporative cooling of metastable AEAs in magnetic traps. Here we present experimental data for 40Ca[4s4p]3 P2 clearly confirming the asserted multichannel character of the collision mechanism. While elastic cross sections are found to be similar to the predicted values, inelastic cross sections exceed the calculations by an order of magnitude. Our results substantiate the expectation of inefficient evaporative cooling.     

Inelastic scattering of tritium-source antineutrinos on electrons of germanium atoms

Processes of the inelastic magnetic and weak scattering of tritium-beta-source antineutrinos on the bound electrons of a germanium atom are considered. The results obtained by calculating the spectra and cross sections are presented for the energy-transfer range between 10 eV and 18 keV.     

Inelastic processes in collisions of multicharged fast ions with atoms

We use the eikonal approximation to develop a general formula for the cross sections of inelastic collisions of multicharged fast ions (including relativistic ions) with atoms that is applicable within a broad range of collision energies, has the standard nonrelativistic limit, and becomes, in the ultrarelativistic case, the well-known result that follows from the exact solution of the Dirac equation. As an example we study the excitation and ionization of a hydrogenlike atom, the single and double excitation and ionization of a heliumlike atom, and multiple (up to the eighth order) ionization of the neon atom and (up to eighteenth order) ionization of the argon atom. We derive simple analytical expressions for the inelastic cross sections and establish recurrence relations linking the cross sections of ionization of different orders. Finally, we compare our results with the experimental data. Zh. éksp. Teor. Fiz. 114, 1646–1660 (November 1998)     

Study of orientation transfer by collisions of the second kind between 198Hg and 199Hg atoms

A double resonance experiment is used to detect the collisional transfer of orientation from an optically oriented ¹⁹⁸Hg (6³P₁) atom to the hyperfine levels $\text{(6}{}^3\text{P}{}_1\text{; F =}\text{1}\text{2}\text{, F =}\text{3}\text{2}\text{)}$ of a ¹⁹⁹Hg atom. The reaction of transfer is assumed to be ¹⁹⁸Hg (6³P₁) + ¹⁹⁹Hg (6¹S₀) → ¹⁹⁸Hg (6¹S₀) + ¹⁹⁹Hg (6³P₁).The theory of such a process is summarized, the experimental set-up described and the double resonance signals compared with those predicted by the theory.     

Inelastic processes in the scattering of metastable rare gas atoms at metal surfaces

Electron spectra of various metastable rare gas atoms systematically measured on a Pt(111) surface with Rb coverages ranging from submonolayers (3%) to multilayers are presented. The different decay channels of the excited particles are discussed in terms of resonant electron exchange processes between the substrate and the projectile in relation to the work function. It is shown that below a certain value of the work function a highly excited negative rare gas atom is formed which can undergo different de-excitation processes. A careful discussion of the branching ratios into the decay channels offers a natural explanation of the variations in the electron spectra induced by alkali metal adsorption. Additionally, an attempt is made to extract information about the alkali metal chemisorption state from the observed electron spectra.     

Spin exchange and chemi-ionization during collisions of polarized metastable helium atoms with ground-state cesium atoms

The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process (spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined experimentally: C _se=(2.8±0.8)×10⁻⁹ cm³s⁻¹, C _ci=(1.0±0.3)×10⁻⁹ cm³s⁻¹. Zh. Tekh. Fiz. 69, 36–40 (September 1999)