Collision physics is currently enjoying an incredibly exciting time as a consequence of recent new experimental advances. One of these advances is the COLTRIMS (cold-target recoil-ion momentum spectroscopy) method which can be used to obtain full three-dimensional pictures of a collision process. These 3D pictures contain very detailed information about the fundamental forces controlling nature on the atomic level and the challenge for theory is to see if our theoretical models can accurately predict what is observed experimentally. One of the most sensitive probes of the important fundamental forces is charged particle ionization of atoms/molecules. The purpose of the NSF funded work is to theoretically examine several open questions in the field of charged particle ionization of atoms and molecules for both the 3-body and 4-body problems and for both electron-impact and heavy-particle impact.
There are several broader impacts for the project. (1) The students who work on this project learn analytical and numerical techniques that are valuable for a career in either academia or industry. (2) The results of this research will be disseminated broadly in leading peer-reviewed journals and presented at scientific conferences. (3) The cutting-edge research will help establish important benchmarks for future research on interactions at the atomic level and it will lead to new theoretical insight on an important topic of fundamental significance. (4) The work will provide theoretical support for at least eight experimental labs (2 NSF funded labs in the US, 2 in Germany, 1 in England, 2 in Australia, and 1 in China). (5) One component of the work is to investigate processes occurring in the constituent components of DNA with a long term objective to obtain an understanding of the effects of radiation damage on biological DNA.
The purpose of the NSF funded work is to explore what can be viewed as one of the most fundamental, unsolved problems in physics, the few-body problem. The few-body problem arises from the fact that the quantum mechanical Schrödinger equation, which determines the behavior of fundamental particles, is not analytically soluble for more than two mutually interacting particles. As a result, for more than two particles, theory must resort to using approximations, the validity of which can only be determined by comparison with experiment. Atomic and molecular collisions present a valuable test of these theoretical treatments of the few-body problem for two main reasons. First, unlike nuclear physics for example, the underlying fundamental interaction between the particles in atomic systems, the electromagnetic force, is known exactly for any two particles. Consequently, for collisions involving more than two particles, discrepancies between experiment and theory must be attributed to the few-body aspects of the theoretical model. Second, recent advancements in experimental techniques have provided complete kinematic information about every particle in the system. These experiments provide a stringent test for theoretical models. During the three year period covered by the grant, several open questions in the field of charged particle ionization of atoms and molecules for both the 3-body and 4-body problems were examined for both electron-impact and heavy-particle impact. The strength of the theoretical model we use lies in the fact that the effect of any two-particle interaction can be isolated and evaluated. By looking at various two-particle interactions, we were able to develop simple understandable models to describe some very complex collisions. One of the long term goals of this work is to be able to accurately predict the outcome of a collision between an electron and molecules of biological interest. The reason for this lies in the fact that secondary electrons produced by ionizing radiation are known to play a significant role in radiation damage to DNA. One of the current approaches for studying radiation damage to DNA is to investigate processes occurring in the constituent components and, in collaboration with an experimental group in Adelaide, Australia, we studied electron-impact ionization of several large molecules either of biological interest or molecules which are DNA analogues. We were very pleased by the fact that our theoretical model yielded reasonably good agreement with the experimental data and we believe that we know how to improve the model in the near future. Consequently, we are hopeful that we can make a significant contribution to this very important health related issue in addition to advancing the understanding of the basic reactions governing few-body processes.
