The resonant Auger spectra of formic acid, acetaldehyde, acetic acid and methyl formate U. Hergenhahn a,b, * ,A.R€ udel a , K. Maier a,b , A.M. Bradshaw b , R.F. Fink c , A.T. Wen d a Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany b Max-Planck-Institut f€ ur Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany c Institut f€ ur Physiologie MA 2/149, Ruhr-Universit€ at Bochum, 44780 Bochum, Germany d Department of Chemistry, SUNY, Stony Brook, NY 11794-3400, USA Received 5 July 2002 Abstract WehavemeasuredtheresonantAugerspectraoffoursimpleorganicmoleculescontainingacarbonyl(C@O)group, following excitation of an oxygen 1s electron to an antibonding valence orbital. The full range of final state energies is presented. The spectra are analysed for similarities arising from similar chemical structures within the molecules. An ab initio calculation of the resonant Auger spectrum of the simplest molecule, formic acid, is shown to aid in the inter- pretation. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 33.80.Eh; 33.60.Cv; 82.50.Kx Keywords: Resonant Auger decay; Formic acid; Acetaldehyde; Acetic acid; Methyl formate; Deexcitation spectrum 1. Introduction Resonant Auger decay is the autoionization of an atomic or molecular state that has been created by excitation of an inner shell electron to an un- occupied valence orbital. In extended systems, such as polyatomic molecules, several inner shell electrons on chemically different sites within the molecule can be excited into valence states. These excitation processes will differ in energy, and therefore, with a tuneable light source, a certain site within the molecule can be selectively excited. In this paper we address the question of the extent to which the shape of a resonant Auger decay spectrum is specific for the chemical environment at the site of the decay process. A first answer can be obtained by making a comparisonwithnormalAugerdecay,whichisthe autoionization of a state created by ionization of an inner shell electron. The properties of the nor- mal Auger spectra of polyatomic molecules have been the subject of a number of experimental and Chemical Physics 289 (2003) 57–67 www.elsevier.com/locate/chemphys * Corresponding author. Fax: +49-30-84-135-603. E-mail address: hergenhahn@fhi-berlin.mpg.de (U. Her- genhahn). 0301-0104/03/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0301-0104(02)00795-4