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J. Phys. Chem. A 2008, 112, 7498–7506
Vibrational Spectroscopy of Nitroalkane Chains Using Electron Autodetachment and Ar Predissociation Holger Schneider,† Kristen M. Vogelhuber,† Florian Schinle,† John F. Stanton,‡ and J. Mathias Weber*,† JILA, NIST, and Department of Chemistry and Biochemistry, UniVersity of Colorado, Boulder, Colorado 80309, and Department of Chemistry and Biochemistry, UniVersity of Texas at Austin, 1 UniVersity Station A5300, Austin, TX 78712-0165 ReceiVed: January 7, 2008; ReVised Manuscript ReceiVed: June 2, 2008
If the binding energy of an excess electron is lower than some of the vibrational levels of its host anion, vibrational excitation can lead to autodetachment. We use excitation of CH stretching modes in nitroalkane anions (2700-3000 cm-1), where the excess electron is localized predominantly on the NO2 group. We present data on nitroalkane anions of various chain lengths, showing that this technique is a valid approach to the vibrational spectroscopy of such systems extending to nitroalkane anions at least the size of nitropentane. We compare spectra taken by using vibrational autodetachment with spectra obtained by monitoring Ar evaporation from Ar solvated nitroalkane anions. The spectra of nitromethane and nitroethane are assigned on the basis of ab initio calculations with a detailed analysis of Fermi resonances of CH stretching fundamentals with overtones and combination bands of HCH bending modes. 1. Introduction Vibrational spectroscopy in concert with quantum chemical calculations is an important way to characterize the structure of ions and to draw conclusions on their interaction with other molecular species as the spectra of bare and solvated ions are compared. For a target of mass-selected ions, it is very hard to use straightforward absorption spectroscopy (i.e., the attenuation of light as it passes through a sample) to obtain an infrared (IR) spectrum because of the low density of mass-selected ion beams (typically
