Outgoing Electrons Research Articles

(e,2e) spectroscopy

Most of our knowledge of the electronic structure of atoms and molecules is derived from excitation energies and transition probabilities. These observable quantities are related to the electronic wave functions by integrals over unmeasured variables. Another observable more directly related to the wave function than energy or transition probability is the single-electron momentum density, the probability that an electron in a well-defined orbital has a given value of momentum. Over the last twenty years a technique has been developed for measuring momentum densities in atoms and molecules. The technique, ([ital e],2[ital e]) spectroscopy, is based on electron-impact ionization with complete determination of the momenta of both incoming and outgoing electrons. The conditions necessary to extract momentum-density information from the ionization experiments are examined and related to general theories of electron scattering. Different experimental arrangements are reviewed and momentum-density results from selected examples are discussed.

Tau --> micro micro micro-bar and tau --> microee-bar decays in string models with E6 symmetry.

A detailed analysis on the rare $\tau$ decay {\it via} $\taumue$ and $\taumus$ in the string models with $\e6$ symmetry is reported. It is found that $\Gamma(\taumue)\sim(6-7)\Gamma(\taumus)$ and these rates are in general about 1000 times less than that of $\Gamma(\mu\rightarrow e\gamma)$. It is also found that the out-going muon in $\taumue$ is almost 100\% right-handed polarized and the out-going electrons would be predominately parallel to each other. These decay processes may be accessible at the SSC.

A new spherical-wave approximation for photoelectron diffraction, EXAFS and MEED

An exact formula for the expansion of an outgoing spherical electron wave around another centre is presented from which new approximation for spherical-wave scattering are derived. These expressions allow a considerably higher accuracy in high-speed numerical multiple-scattering calculations than methods existing hitherto. This is demonstrated for tungsten in the energy range from 50 to 5000 eV. The improvements of the given formulae over earlier approaches are greater the higher the energy. In particular the errors in the forward scattering direction are very small.

Theory of a two-level system interacting with a degenerate electron gas. I. Partition function.

The problem of the two-level system (TLS) interacting with a free-electron gas is considered. In a previous work Yu and Anderson treated that problem by taking into account the screening by the conduction electrons described by an arbitrarily large phase shift. The present paper is devoted to a generalization of their result by including weak electron-assisted TLS transition processes. Generalizing the Yuval-Anderson technique, the partition function is derived, which has the form of the partition function of a one-dimensional Coulomb gas with logarithmic interactions. The charges introduced depend on the phase shifts and on the electron spin and orbital quantum numbers corresponding to the incoming and outgoing electrons in the related electron-TLS scattering processes. Additionally charged dipoles are introduced to describe those processes in which the scattered electrons do not change their quantum number. Special care is paid to the formal divergencies occurring in these processes if the long-time asymptotic expressions are used for the conduction-electron Green's functions. In this way, going beyond the charge-charge interaction, charge-dipole and dipole-dipole interactions are introduced. The next paper deals with the derivation of the scaling equations, which are derived by eliminating the short-time behavior.

Widths of 2S, 2Po, and 2D resonances in Li I, Be II, and B III.

The autoionization widths of the lower $^{2}\mathrm{S}$, ${}^{2}$${P}^{o}$, and $^{2}\mathrm{D}$ Feshbach resonances in Li i, Be ii, and B iii are calculated with the saddle-point complex-rotation method. For Be ii and B iii the radiation widths are also computed. Relativistic and mass polarization corrections to the resonance energy are included. The width results for the [1s(2s2p)${}^{3}$P]${}^{2}$${P}^{o}$ and (1s2p2p)${}^{2}$D states are compared with other theoretical results and with the recently published experimental results for Li i and Be ii. Transition wavelengths involving these autoionizing states are also calculated and compared with theory and experiment. Due to the substantial difference between theory and experiment on the Li[1s(2s2p)${}^{3}$P]${}^{2}$${P}^{o}$ width, a detailed study is made on the convergence of this width with respect to the closed channel, open-channel target state and out-going electron wave function to access the stability and reliability of the theoretical result.

Absolute triple differential cross sections for electron impact ionization of helium: Comparison between experimental and theoretical results at 256 eV collision energy

Triple differential cross sections have been measured for electron impact ionization of helium at 256 eV collision energy, 3 eV energy of the slow outgoing electrons and scattering angles of the fast outgoing electrons of 4°, 6°, 8°, and 10°. The data have been put on absolute scale by extrapolating the generalized oscillator strength to zero momentum transfer. In this optical limit the triple differential cross sections can be normalized by using the well-known cross sections for photoionization.