Electron-atom scattering ionization

Angular Correlation in Multiphoton Ionization of Atoms, S. J. Smith and G. Leuchs Optical Pumping and Spin Exchange in Gas Cells, R. J. Knize, Z. Hit, and W. Mapper Correlations in Electron-Atom Scattering,... 

The interaction of even simple diatomic molecules with strong laser fields is considerably more complicated than the interaction with atoms. In atoms, nearly all of the observed phenomena can be explained with a simple three-step model [1], at least in the tunneling regime (1) The laser field releases the least bound electron through tunneling ionization (2) the free electron evolves in the laser field and (3) under certain conditions, the electron can return to the vicinity of the ion core, and either collisionally ionize a second electron [2], scatter off the core and gain additional kinetic energy [3], or recombine with the core and produce a harmonic photon [4]. 

Lastly, we mention one more excitation mechanism that has been observed in molecules. It is well-established that following strong field ionization in atoms and molecules, under certain conditions, the ionized electron can be driven back to the ion core where it can recombine to produce high-harmonic radiation, induce further ionization, or experience inelastic scattering. However, there is also the possibility of collisional excitation. Such excitation was observed in [43] in N2 and O2. In both molecules, one electron is tunnel ionized by the strong laser field. When the electron rescatters with the ion core, it can collisionally ionize and excite the molecular ion, creating either N + or Ol+ in an excited state. When the double ion dissociates, its initial state can... 

Fig. 5.8. The triple differential cross section for positron impact ionization of atomic hydrogen, expressed as a function of the energy of the ejected electron. The scattered positron and electron both emerge in the direction of the incident...

One-electron atoms subjected to a time-dependent external field provide physically realistic examples of scattering systems with chaotic classical dynamics. Recent work on atoms subjected to a sinusoidal external field or to a periodic sequence of instantaneous kicks is reviewed with the aim of exposing similarities and differences to frequently studied abstract model systems. Particular attention is paid to the fractal structure of the set of trapped unstable trajectories and to the long time behavior of survival probabilities which determine the ionization rates of the atoms. Corresponding results for unperturbed two-electron atoms are discussed. 

The upward-directed electric field accelerates the ambient thermal energy electrons of mean energy = 1.5 kT to a new distribution fimction that depends upon the local E field and neutral composition and density. The connection between the spatial E field and the electron energy distribution function is made through solution of either the Boltzmann equation (Pitchford et al., 1981 Phelps and Pitchford, 1985) or the derived Fokker-Planck equation (Milikh et al., 1998a). In either case, a full database of cross sections for electron-molecule (N2, O2) excitation, ionization (both direct and dissociative), and attachment (for O2) is needed for reliable solutions. Electron-ion and electron-atom (N, O) scattering are usually neglected because of the small product of electron and ion or atom densities. 

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