M. L. Du

Modifying the photodetachment near a metal surface by a weak electric field

We show the photodetachment cross sections of H-near a metal surface can be modified using a weak static electric field. The modification is possible because the oscillatory part of the cross section near a metal surface is directly connected with the transit time and the action of the detached electron closed-orbit which can be changed systematically by varying the static electric field strength. Photodetachment cross sections for various photon energies and electric field values are calculated and displayed.

Predissociation channels of the C 3Πg Rydberg state of O2

A theoretical formulation is presented of the predissociation of vibrational levels of the C 3Πg Rydberg state of O2 in terms of an inhomogeneous driven equation which takes account of couplings between the Rydberg state and the lowest two 3Πg valence states and the coupling between the valence states. The branching ratios for decay to the end products O(3P)+O(1D) and O(3P)+O(3P) are obtained and it is found that by a suitable choice of potential energy curves and coupling interactions agreement can be obtained with the experimental data. Utility of the Landau–Zener model is investigated and it is shown to be highly successful in describing the decay paths of the low‐lying vibrational levels but it fails for the high‐lying levels because of the occurrence of quantal interference between the channels. It is demonstrated that because of flux conservation the total width of the Rydberg vibrational state is independent of the coupling between the valence states.

Enhancement of bichromatic high-order-harmonic generation with a high-frequency field

Using a high-frequency field superposed to a linearly polarized bichromatic laser field composed by a wave with frequency omega and a wave with frequency 2 omega, we show it is possible to enhance the intensity of a group of high harmonics in orders of magnitude. These harmonics have frequencies about 30% higher than the monochromatic-cutoff frequency, and, within the three-step-model framework, correspond to a set of electron trajectories for which tunneling ionization is strongly suppressed. Particular features in the observed enhancement suggest that the high-frequency field provides an additional mechanism for the electron to reach the continuum. This interpretation is supported by a time-frequency analysis of the harmonic yield. The additional high-frequency field permits the control of this group of harmonics leaving all other sets of harmonics practically unchanged, which is an advantage over schemes involving only bichromatic fields.

Level shifts of discrete states embedded in a continuum

A procedure which offers computational advantages over the customary formalism is presented for calculating the shifts of the energy levels of discrete states embedded in a continuum. Numerical procedures are described and applied to the vibrational level shifts of the B 3Σ−u state of 16O2 interacting with the 5Πu continuum.

Log-derivative methods based on linear two-step integration formulae

Single- and multi-channel propagators for the log-derivative and a simple modification of it are derived from the linear two-step formulae of Hartree and Numerov. Their stabilities are briefly discussed. Their use is illustrated in a single-channel eigenvalue problem and in a multi-channel scattering problem.

Amplitude method for multichannel resonances

An amplitude method is described for determining the partial and total widths and the energies of resonances in multichannel processes in which resonance states may decay into many channels. The method is tested by application to a model problem and by a study of the predissociation of the C 3Πg Rydberg state of O2.

Formula for laser pulse photodetachments of negative ions

We express the detachment cross section caused by a Gaussian pulsed laser in terms of that caused by a continuous laser. Using this expression and Poissons summation formula, we derive a uniform semiclassical formula for the cross section of pulsed-laser photodetachment of a hydrogen ion H- in Static parallel electric and magnetic fields. The uniform semiclassical formula does not have a divergence problem at the bifurcation points. Numerical comparisons show an excellent agreement between the uniform semiclassical formula and the quantum formula for the detachment cross section.

A note on Cooley's energy correction formula

Abstract A simple alternative derivation based on standard first-order perturbation theory in quantum mechanics is given for Cooleys energy correction formula which is employed in the popular iterative Numerov-Cooley method for numerically solving the one-dimensional eigenvalue Schrodinger equation.

A numerical method for the calculation of transmission coefficient

A numerical method is presented for calculating the quantum-mechanical transmission coefficient of one-dimensional problems with potentials of arbitrary shapes. The method is demonstrated to give very accurate results on two solvable examples. The numerical error in the calculated transmission coefficient is proportional to the second power of integration step size for potentials without discontinuities; for potentials with discontinuities, the dependence is linear.

RENORMALIZED METHOD FOR MULTICHANNEL INHOMOGENEOUS SCHRODINGER-EQUATIONS

A renormalized method is developed for the solution of multichannel inhomogeneous Schrodinger equations that appear frequently in atomic and molecular physics. The method is stable and accurate, its derivation is straightforward. Formulae are presented in both the Hartree and Numerov approximations. A numerical example is used to demonstrate the method.