Momentum Distributions Of Ejected Electrons Research Articles

Ultra-fast spin dynamics in the 2s2p2 configuration of C+ studied by time-dependent R-matrix theory

We employ time-dependent R-matrix theory to study ultra-fast dynamics in the doublet 2s2p2 configuration of C+ for a total magnetic quantum number M = 1. In contrast to the dynamics observed for M = 0, ultra-fast dynamics for M = 1 is governed by spin dynamics in which the 2s electron acts as a flag rather than a spectator electron. Under the assumption that mS = 1/2, m2s = 1/2 allows spin dynamics involving the two 2p electrons, whereas m2s = −1/2 prevents spin dynamics of the two 2p electrons. For a pump–probe pulse scheme with ℏωpump = 10.9 eV and ℏωprobe = 16.3 eV and both pulses six cycles long, little sign of spin dynamics is observed in the total ionization probability. Signs of spin dynamics can be observed, however, in the ejected-electron momentum distributions. We demonstrate that the ejected-electron momentum distributions can be used for unaligned targets to separate the contributions of initial M = 0 and M = 1 levels. This would, in principle, allow unaligned target ions to be used to obtain information on the different dynamics in the 2s2p2 configuration for the M = 0 and M = 1 levels from a single experiment.

Limitations of the strong field approximation in ionization of the hydrogen atom by ultrashort pulses

We present a theoretical study of the ionization of hydrogen atoms as a result of the interaction with an ultrashort external electric field. Doubly-differential momentum distributions and angular momentum distributions of ejected electrons calculated in the framework of the Coulomb-Volkov and strong field approximations, as well as classical calculations are compared with the exact solution of the time dependent Schr odinger equation. We show that in the impulsive limit, the Coulomb-Volkov distorted wave theory reproduces the exact solution. The validity of the strong field approximation is probed both classically and quantum mechanically. We found that classical mechanics describes the proper quantum momentum distributions of the ejected electrons right after a sudden momentum transfer, however pronounced the differences at latter stages that arise during the subsequent electron-nucleus interaction. Although the classical calculations reproduce the quantum momentum distributions, it fails to describe properly the angular momentum distributions, even in the limit of strong fields. The origin of this failure can be attributed to the difference between quantum and classical initial spatial distributions.

Advanced adiabatic approximation for momentum distributions of ejected electrons in slow atomic collisions

The problem of determination of momentum distributions of ejected electrons in slow atomic collisions is studied within the impact-parameter method by using a dynamic adiabatic basis which takes into account the correct boundary conditions. An expression is obtained which relates the momentum distribution of the ejected electrons with a coherent sum of the delocalized dynamic adiabatic eigenstates (elementary wavepackets). The form of the momentum distribution exactly coincides with the form of the total wavepacket in configuration space. General formulas are applied to a model problem of electron detachment in the process \(\) in which the electron-atom interactions are described by the zero-range potentials. In the example considered, the momentum distribution of ejected electrons, in the center-of-mass frame, exhibits a maximum located in the scattering plane on the circle of radius \(\) (in atomic units), where v is the relative collision velocity and \(\) is the impact parameter.

Quantum mechanical calculation of ejected electron spectra for ion-atom collisions

We present a quantum mechanical method for calculating the ejected electron probability distribution in ion-atom collisions. The time-dependent Schrödinger equation, formulated with a classical straight-line trajectory for the internuclear motion, is integrated directly on a two-centre momentum space grid. The time-dependent wavefunction at large internuclear separation is analysed to extract the ejected momentum distribution as well as excitation and charge transfer amplitudes. Calculations have been performed at collision velocities of 1, 2 and 5 au for proton and antiproton collisions with atomic hydrogen, at a few impact parameters. Excitation and charge transfer probabilities are also calculated to check against results obtained from the close-coupling method. The ejected electron momentum distributions are shown.

Single ionization of He by low-velocity protons and C6+: Ejected electron momentum distributions.

A technique for electron spectroscopy which yields full two-dimensional momentum distributions for continuum electrons has been used to study ejected electrons from single ionization of He by ${\mathrm{C}}^{6+}$ and proton projectiles at low velocities. Projectile velocities of 1.63, 1.38, and 1.16 a.u. for ${\mathrm{C}}^{6+}$ and 2.39, 1.71, 1.15, .85, and 0.63 a.u. for protons were used. All spectra show much broader distributions along the beam than transverse to the beam. For the case of proton bombardment, the spectra are strongly influenced by both target and projectile potentials, maximizing near the velocity of the saddle in the potential between the two receding ion cores for the lowest projectile velocities. For ${\mathrm{C}}^{6+}$ projectiles, the spectra appear to be dominated by the projectile potential and the center of the distribution is strongly shifted toward the projectile velocity. Theoretical results from the continuum-distorted-wave--eikonal-initial-state and classical-trajectory--Monte Carlo methods are in rather good agreement with the proton data but do not agree well with the ${\mathrm{C}}^{6+}$ data. \textcopyright{} 1996 The American Physical Society.