Spectroscopy and ionization thresholds of π-isoelectronic 1-phenylallyl and benzylallenyl resonance stabilized radicals

Joshua A. Sebree, Nathanael M. Kidwell, Evan G. Buchanan, Marek Z. Zgierski, Timothy S. Zwier
2011 Chemical Science  
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more » ... ectronic 1-phenylallyl and benzylallenyl resonance stabilized radicals Sebree, Joshua A.; Kidwell, Nathanael M.; Buchanan, Evan G.; Zgierski, Marek Z.; Zwiera, Timothy S. https://publications-cnrc.canada.ca/fra/droits L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site 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 -D 1 origin of the 1-phenylallyl radical is at 19208 cm -1 , with extensive vibronic structure extending 10 over 2000 cm -1 above the D 1 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 15 ~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 D 0 -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 D 1 20 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. 65 phenylallyl radical (C 9 H 9 ) exists in two isomeric forms (1trans-1-phenylallyl radical cis-1-phenylallyl radical 2-phenylallyl radical
doi:10.1039/c1sc00246e fatcat:zrn2p4ngvva2vm35d2mojah6da