Paper SS-ThP12
Synchrotron Radiation-Induced Reactions of Astrochemical Interest*

Thursday, October 23, 2008, 6:00 pm, Room Hall D

In molecular cloud regions of the interstellar medium (ISM), astronomical observations have revealed a rich chemistry with the detection of over 130 different chemical species ranging from simple diatomic molecules to complex organic molecules such as polycyclic aromatic hydrocarbons (PAHs). These molecules may have been involved in the prebiotic chemistry that led to life’s origin. Our approach for simulating such chemistry is to in-situ monitor the x-ray induced chemical reactions of model compounds adsorbed on well-characterized substrates. We are currently pursuing two areas of research in this field. The first one is to understand the source of chirality in prebiotic molecules, which is a subject of great interest to a wide group of researchers. We have recently demonstrated that low-energy spin-polarized secondary electrons, produced by irradiation of a magnetized permalloy substrate can induce chiral selective chemistry of adsorbed (R)- or (S)-2-butanol on permalloy.¹ Using x-ray photoelectron spectroscopy (XPS) to monitor the intensity of the C-O peak, the results showed an enhancement of ~10% in the rate of C-O bond cleavage that depends on the chirality of the molecule and the spin polarization of the substrate secondary electrons. In addition to the C1s XPS measurements used to determine the rate constants, O1s XPS and O1s near edge x-ray absorption fine structure (NEXAFS) as well as x-ray magnetic circular dichrosim (XMCD) measurements were performed. The second area of research is the investigation of x-ray induced chemical reactions of PAHs which are flat molecules based on rings of six carbon atoms. PAHs are of particular interest because they are often used as biomarkers that indicate life. A large variety of these molecules has been detected in meteorites after being delivered to Earth. We will present some preliminary results on the x-ray induced reactions of coronene (C₂₄H₁₂). The focus of this work will be to understand the kinetics and mechanisms of this system, as well as other PAHs. Experiments were performed under UHV conditions utilizing both XPS and x-ray excited optical luminescence (XEOL) to monitor the reactions.

*This work was performed at the Advanced Photon Source and was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357.
¹ R.A. Rosenberg, M. Abu Haija and P.J. Ryan, to be published.