Current Research

    This electron scattering group has focused its attention on gas phase studies of temporary negative ion formation and decay in complex molecules. These transient species, having lifetimes in the 10^-12 to 10^-15 second range, are formed when an impinging electron occupies a normally empty molecular orbital. Such “resonances” dominate many electron scattering processes at energies from 0 to 10 eV. In particular, the presence of an electron in an antibonding orbital weakens the bond strengths causing the molecule to deform during the lifetime of the “resonance”. Upon autodetachment of the electron, the molecule may be left in a vibrationally excited state. In fact, temporary negative ion states are very efficient at exciting vibrational motion.
    Currently the group is examining the dissociative electron attachment (DEA) process, a second means by which temporary negative ions may decay. In this reaction, a fragment having a positive electron affinity may carry off the temporarily bound electron, forming a neutral free radical and a permanent anion. This process is particularly important in halogenated hydrocarbons, such as those used in plasma etching. The DEA cross section is extraordinarily sensitive to many molecular parameters that are quite difficult to calculate, and thus, there exist no theoretical cross sections in systems larger than diatomics. The dynamic range of these cross sections can be enormous. In the series of chloromethanes, for example, peak cross sections vary by more than a factor of 10⁶ with increasing chlorination.
Current emphasis is on molecules of biological interest such as the DNA bases and amino acids.

Recent Key Publications

A. M. Scheer, K. Aflatooni, G. A. Gallup and P. D. Burrow, “Bond Breaking and Temporary Anion States in Uracil and Halouracils: Implications for the DNA Bases”, Phys. Rev. Lett. 92, 068102 (2004).

J.P. Sullivan, P. D. Burrow, D.S. Newman, K. Bartschat, J.A. Michejda, R. Panajotovic, M. Moghbelalhossein, R.P. McEachran and S.J. Buckman, “An Experimental and Theoretical Study of Transient Negative Ions in Mg, Zn, Cd and Hg”, New Journal of Physics 5, 159 (2003).

K. Aflatooni, G. A. Gallup and P. D. Burrow, “Temporary Anion States of closo-Carboranes and Diethyl Carborane”, J. Phys. Chem. A 106, 4703 (2002).

Recent Graduates and Current Affiliations

Kayvan Aflatooni, Ph.D., 1998, Assistant Prof., Fort Hays State University, Hays, KS.
Thesis: “Temporary Negative Ion States and Dissociative Attachment in Dichloroalkanes”