Person:

Kharchenko, Vasili

Hydrogen is of critical importance in atomic and molecular physics and the development of a simple and efficient technique for trapping cold and ultracold hydrogen atoms would be a significant advance. In this study we simulate a recently proposed trap-loading mechanism for trapping hydrogen atoms released from a neon matrix. Accurate ab initio quantum calculations are reported of the neon-hydrogen interaction potential and the energy- and angular-dependent elastic scattering cross sections that control the energy transfer of initially cold atoms are obtained. They are then used to construct the Boltzmann kinetic equation, describing the energy relaxation process. Numerical solutions of the Boltzmann equation predict the time evolution of the hydrogen energy distribution function. Based on the simulations we discuss the prospects of the technique.

Collision energy transfer processes between hydrogen, deuterium, and oxygen atoms in the upper atmospheres of the terrestrial planets are studied. A new set of interaction potentials has been constructed using an accurate ab initio method. Full orientation-dependent scattering cross sections have been obtained quantum mechanically and have been incorporated into the construction of the linear Boltzmann kinetic equation describing the energy relaxation process. The isotope and temperature dependence of the energy relaxation parameters have been analyzed. Distributions of the secondary energetic recoil atoms have been computed and the fractions of hot atoms capable of escaping from the atmospheres of the terrestrial planets have been determined. For applications to atmospheric physics and astrophysics, we have computed effective hard sphere cross sections for O + H and O + D collisions that closely reproduce the energy relaxation kinetics obtained from the linear Boltzmann equation. These effective cross sections, which are functions of the laboratory frame collisional energy and the temperature of the bath gas, may be used in simulations of the thermalization of hot O, H, and D atoms and their escape from planets.

A new and more comprehensive model of charge-exchange induced X-ray emission, due to ions precipitating into the Jovian atmosphere near the poles, has been used to analyze spectral observations made by the Chandra X-ray Observatory. The model includes for the first time carbon ions, in addition to the oxygen and sulfur ions previously considered, in order to account for possible ion origins from both the solar wind and the Jovian magnetosphere. By comparing the model spectra with newly reprocessed Chandra observations, we conclude that carbon ion emission provides a negligible contribution, suggesting that solar wind ions are not responsible for the observed polar X-rays. In addition, results of the model fits to observations support the previously estimated seeding kinetic energies of the precipitating ions (~0.7-2 MeV u(^{–1})), but infer a different relative sulfur-to-oxygen abundance ratio for these Chandra observations.