Classical and semiclassical calculations of state-selective cross sections for electron capture and excitation in Be4++ H(2s) collisions

A computational study of Be4++H(2s) collisions has been carried out. Two computational models have been employed: the classical trajectory Monte Carlo (CTMC) method and the numerical solution of the time-dependent Schrödinger equation (GTDSE). The integral n and nl partial cross sections for H excitation and electron capture, obtained with both methods, are compared at two energies: 20 and 100 keV/u. It is shown that the CTMC, with an improved hydrogenic initial distribution, provides excitation cross sections in good agreement with the numerical calculation for excitation to H(n) with n>3. The agreement between the corresponding nl partial cross sections from both methods is less satisfactory at 100 keV/u, where there is a transition from the low-energy mechanism that involves an increase of the populations with l, and the high-energy mechanism, where the dipole-allowed transitions are dominant. The electron capture cross sections calculated with the CTMC method do not depend on the initial distribution and show a reasonable agreement with the GTDSE ones, which supports the use of the CTMC method to calculate electron capture cross sections into highly excited levels and total cross sections. The mechanism of the electron capture process is discussed and CTMC calculations of the ionization process are also presente

Charge Transfer and Electron Production in Proton Collisions with Uracil: A Classical and Semiclassical Study

Cross sections for charge transfer and ionization in proton–uracil collisions are studied, for collision energies (Formula presented.) keV, using two computational models. At low energies, below 20 keV, the charge transfer total cross section is calculated employing a semiclassical close-coupling expansion in terms of the electronic functions of the supermolecule (H-uracil) (Formula presented.). At energies above 20 keV, a classical-trajectory Monte Carlo method is employed. The cross sections for charge transfer at low energies have not been previously reported and have high values of the order of 40 Å (Formula presented.), and, at the highest energies of the present calculation, they show good agreement with the previous results. The classical-trajectory Monte Carlo calculation provides a charge transfer and electron production cross section in reasonable agreement with the available experiments. The individual molecular orbital contributions to the total electron production and charge transfer cross sections are analyzed in terms of their energies; this permits the extension of the results to other molecular targets, provided the values of the corresponding orbital energies are know

Procesos de intercambio de carga (Radiativos y no radiativos) en colisiones Ion-Atomo

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias. Departamento de Química Física y Química Cuántica. Fecha de lectura: 30-01-198