Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

Marissa L. Weichman, Jessalyn A. DeVine, Daniel S. Levine, Jongjin B. Kim, Daniel M. Neumark

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm-1 resolution. Isomer selection of the anions is achieved using gasphase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The groundstate bands yield electron affinities and vibrational frequencies for several Franck-Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck-Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.

Original languageEnglish (US)
Pages (from-to)1698-1705
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume113
Issue number7
DOIs
StatePublished - Feb 16 2016

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Anion photoelectron spectroscopy
  • Polycyclic aromatic hydrocarbons
  • Velocity-map imaging
  • Vibronic structure

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