Faculty Publications

Spectroscopy and Ionization Thresholds of π-isoelectronic 1-phenylallyl and benzylallenyl Resonance Stabilized Radicals

Document Type

Article

Journal/Book/Conference Title

Chemical Science

Volume

2

Issue

9

First Page

1746

Last Page

1754

Abstract

Mass-selective two-color resonant two-photon ionization (2C-R2PI) spectra of two resonance stabilized radicals (RSRs), 1-phenylallyl and benzylallenyl radicals, have been recorded under jet-cooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The D 0-D1 origin of the 1-phenylallyl radical is at 19208 cm-1, with extensive vibronic structure extending over 2000 cm -1 above the D1 origin. Much of this structure is assigned based on comparison with DFT and TDDFT calculations. Two-color photoionization efficiency scans reveal a sharp ionization threshold, providing a precise adiabatic ionization potential for the radical of 6.905(2) eV. By comparison, the benzylallenyl radical has an electronic origin at 19703 cm-1 and Franck-Condon activity similar to phenylallyl. The photoionization efficiency curve shows a gradual onset with apparent threshold at ∼7.50(2) eV. Visible-visible holeburning was used to show that each radical exists in one isomeric form in the expansion. The CH stretch IR spectrum of each radical was taken using D0-resonant ion dip infrared spectroscopy (D 0-RIDIRS) in a novel four-laser experiment. Comparison of the IR spectrum with the predictions of DFT B3LYP calculations leads to firm assignment of each radical as the trans isomer. TDDFT calculations on the excited states of benzylallenyl suggest the possibility that the excited state levels originally excited convert to an all-planar form prior to ionization. The potential role that these radicals could play in Titan's atmosphere as intermediates in formation pathways for polycyclic aromatic hydrocarbons (PAHs) is briefly discussed. © The Royal Society of Chemistry 2011.

Department

Department of Chemistry and Biochemistry

Original Publication Date

9-1-2011

DOI of published version

10.1039/c1sc00246e

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