Electron-molecule interactions initiate and drive almost all chemical processes relevant to areas such as radiation damage, environmental chemistry, industrial plasmas used in the processing of materials for microelectronics and in modern lighting applications. Recently, there has also been an increasing awareness of the importance of electron-molecule interactions in biological systems. For example, low-energy electrons seem to have a significant effect in driving DNA strand breaks due to the passage of ionizing radiation through biological material. Given the prominence of electron-molecule interactions in many environments, it is imperative that we understand how electron interactions drive chemical processes, particularly those that lead to bond breaking in molecules, as the remaining fragments often serve as progenitors to chemical reactions and reaction chains. It is also important to understand how energy flows into and out of molecular systems. It is this energy flow that governs the dynamics of any electron-molecule interaction. Given advancements in modern computational resources, theoretical models are poised to address electron interactions with more complex systems, that is, those of more that two or three atoms. However it is difficult to assign any level of confidence to the outcomes of these models due to the sparsity of experimental measurements to benchmark against. This project will measure the bond breaking and molecular dynamics driven in electron interactions with several complex molecular systems, for example, hydrocarbons, alcohols, and simple organic molecules, to serve as experimental benchmarks to theoretical models.
The interactions of electrons with the complex systems above reveal information about the structure and dynamics when driven to non-equilibrium states. By exploring both high- and low-energy electron interactions, with these complex systems, we can ascertain a more in-depth understanding of the physics driving the correlated dynamics. This project brings the application of the momentum fragment imaging apparatus at Auburn University to the study of correlated dynamics in electron-molecule interactions. The momentum imaging technique measures the full three-dimensional momentum of dissociation fragment ions as a result of electron interaction. This allows for a complete study of dissociation dynamics as a function of both electron energy and interaction angle with respect to a bond axis. It also allows for a measurement of the energy partitioning between translational and internal ro-vibrational energy of dissociating fragment ions. At low electron energies, dissociative electron attachment (DEA) is dependent on the incidence angles of electrons, with respect to particular bond axes, and selectivity of bond cleavage can be realized. Recent results for DEA show that complex stretching and bending dynamics, beyond a quasi-diatomic representation, must be accounted for to adequately explain the dissociation dynamics of triatomic systems. This project will extend previous work by transitioning to more complex systems, as mentioned above, that have seen little or no previous experimental attention. At higher electron energies, the structure and dynamics of select diatomic and triatomic systems driven into highly excited and ionic states will also be probed via momentum imaging of ions formed by the dissociative ionization and ion-pair processes. At both the low- and high-energy regimes, these various processes exhibit constant energy transfer. It is this constant energy transfer that allows for the specific determination of states involved in these processes.
