We have performed extensive close-coupling calculations to obtain total impact ionization cross sections of He atoms by antiprotons at energies from 1 keV to 300 keV by expanding the time-dependent two-electron wave functions in terms of helium eigenstates. The stability of the calculated ionization probabilities and total ionization cross sections with respect to the choice of basis functions ...

In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric fie...

Observations of double ionization by femtosecond-scale near-optical laser pulses with intensities above about 10W/cm revealed a prominent surprising feature. The doubly ionized ion count, as a function of incident laser intensity, was observed to be significantly above the value predicted by the famous ADK ionization formula [1], which is used to describe non-correlated tunneling escape of two ...

The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electro...

The results of rotationally resolved resonance enhanced multiphoton ionization photoelectron spectroscopy and zero kinetic energy-pulsed field ionization studies on HBr via various rotational levels of the F D2 and f D2 Rydberg states are reported. These studies lead to an accurate determination of the lowest ionization threshold as 94 098.961 cm. Observed rotational and spin–orbit branching ra...

Ionization dynamics of resonantly excited helium nanodroplets have been studied by intense XUV light. By doping the nanodroplets with atoms that either attach to the surface or submerge into the center of the droplet, one can study the dynamics of excitation and ionization through the droplet. When resonantly exciting the droplet, we observe a strong ionization enhancement for atoms attached to...

We report time-resolved electron emission in experiments on ionization of rubidium Rydberg atoms (n=90) by few-cycle radio-frequency (RF) (1-10 MHz) pulses. The electron emission occurs in multiple bursts and strongly depends on the carrier-envelope phase as well as the duration and amplitude of the RF pulses. Remarkably, ionization is observed during a series of cycles with the same amplitude....

We propose a new approach to obtain molecular frame photoelectron angular distributions from molecules ionized by intense laser pulses. With our method we study the angular tunnel ionization probability of H2 at a wavelength of 800 nm over an intensity range of 2-4.5 x 10(14) W/cm2. We find an anisotropy that is stronger than predicted by any existing model. To explain the observed anisotropy a...

Direct dissociative ionization is the simplest three-body breakup process in H2. We describe the experimental verification of direct dissociative ionization to the repulsive A2Sigma(+)(u) state by resolving the kinetic energy and angular distributions of the formed protons. A (2+1) resonant enhanced multiphoton ionization process via the isotropic E,F (1)Sigma(+)(g)(v = 6,J = 0) level is employ...

The double ionization of helium in bichromatic, circularly polarized intense laser fields is analyzed with a classical ensemble approach. It is found that counterrotating fields produce significant nonsequential double-ion yield and drive novel ionization dynamics. It is shown that distinct pathways to ionization can be modified by altering the relative intensities of the two colors, allowing f...