Physics Department News Archive

August 13, 2008

Undergraduate Research Described in an Invited Talk

Ft. Worth, TX - Work done by several Augustana College physics students was featured today during an invited talk at the 20th International Conference on the Application of Accelerators in Research and Industry. On behalf of the collaboration, Eric Wells (Assistant Professor of Physics) described experiments measuring the relative probability of producing H2+ and H3+ molecular ions during the dissociation of ammonia and methane.

H3+ is the simplest triatomic molecule, and therefore is a benchmark system for quantum chemists. It has also been drawing recent astrophysical interest since its discovery in molecular clouds and the diffuse intersteller medium, as well as its usefulness in characterizing Jupiter's atmosphere from Earth. The origin of H3+ is these environments is not yet well understood. Recent work has described how it can be produced during collisions between heavy ions and larger molecules such as methanol or even some amino acids, suggesting that the protons in these molecules are more delocalized than originally thought.

Augustana students, along with colleagues at Kansas State University, sought out to study this by comparing the amount of H3+ production from ammonia and methane. One would expect more production from methane, since the CH4 configuration has 4 possible ways to make H3+ triangles, while the NH3 configuation of ammonia has only one. Surprisingly, H3+ was more likely to be produced from ammonia.

Bethany Jochim, a sophomore from Pierre, was able to provide a partial answer to this puzzle. By calculating the symmetric stretch of the NH3+ potential energy surface and comparing it with the same calcuation in CH4+, Jochim showed that it was plausible that a more likely dissociation path existed in the ammonia case. To make these calculations, Jochim used fifth-order Moller-Plesset perturbation theory with a correlation-consistent polarized valence double-zeta basis set. Eduardo Montenegro, a professor from Pontificia Universidade Catolica in Rio de Janeiro, called the theoretical work impressive after the presentation, saying it was "good to show how the calculations match the experiment." Further theoretical analysis is underway.

The experimental work was carried out at the J.R. Macdonald Laboratory by Augustana College students Laura Doshier ('07, now at USD medical school) and Amy Lueking ('07, also at USD medical school) along with Kansas State University students Eli Parke ('07, now at University of Wisconsin) and Mat Leonard ('06, now at the University of California-Berkeley). Parke won an Goldwater Scholarship and was selected to give an invited talk at the 2007 DAMOP meeting in Calgary on behalf of the collaboration. Initial theoretical work was done by Augustana student Sharayah Carey. Faculty members for the Augustana-KSU collaboration are Eric Wells, Kevin Carnes, and Itzik Ben-Itzhak. Initial results and some technical details will be published in the associated conference proceedings. The collaboration expects a more detailed publication to follow when the theoretical analysis is complete.

This work was supported by Research Corporation, the National Science Foundation through award PHY-0653598, and by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Science, US Department of Energy. S.C. and E.W. received additional support provided by the National Science Foundation - Undergraduate Research Center program: CHE-0532242 “The Northern Plains Undergraduate Research Collaboration (NPURC)".

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Theoretical analysis of H3+ production in ammonia. The top figure shows the equillibrium positon for the NH3+ ion. Subsequent figures show the evolution along the ionic potential energy surface to the dissociation limit. Blue is lower electron density, red is higher electron density.