Photoionization of Propargyl and Bromopropargyl Radicals: A Threshold Photoelectron Spectroscopic Study

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 115; no. 11; pp. 2225 - 2230
• Main Authors: Hemberger, Patrick, Lang, Melanie, Noller, Bastian, Fischer, Ingo, Alcaraz, Christian, Cunha de Miranda, Bárbara K, Garcia, Gustavo A, Soldi-Lose, Héloïse
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.03.2011
• Subjects: A: Kinetics, Spectroscopy; Chemical Sciences; or physical chemistry; Theoretical and
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp112110j

In this Article, we present mass-selected threshold photoelectron spectra of propargyl as well as the 1- and 3-bromopropargyl radicals. The reactive intermediates were produced by flash pyrolysis of suitable precursors and ionized by VUV synchrotron radiation. The TPES of the propargyl radical was simulated using data from a recent high-level computational study. An ionization energy (IE) of 8.71 ± 0.02 eV was obtained, in excellent agreement with computations, but slightly above previous experimental IEs. The pyrolysis of 1,3-dibromopropyne delivers both 1- and 3-bromopropargyl radicals that can be distinguished by their different ionization energies (8.34 and 8.16 eV). To explain the vibrational structure, a Franck−Condon simulation was performed, based on DFT calculations, which can account for all major spectral features. Bromopropargyl photoionizes dissociatively beginning at around 10.1 eV. Cationic excited states of 1- and 3-bromopropargyl were tentatively identified. The dissociative photoionization of the precursor (1,3-dibromopropyne) was also examined, delivering an AE0K (C3H2Br+/C3H2Br2) of 10.6 eV.