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Title: Generation of Free Oxygen Atoms O(3P) in Solution by Photolysis of 4-Benzoylpyridine N-Oxide

Laser flash photolysis of 4-benzoylpyridine N-oxide (BPyO) at 308 nm in aqueous solutions generates a triplet excited state 3BPyO* that absorbs strongly in the visible, λmax 490 and 380 nm. 3BPyO* decays with the rate law kdecay/s-1 = (3.3 ± 0.9) × 104 + (1.5 ± 0.2) × 109 [BPyO] to generate a mixture of isomeric hydroxylated benzoylpyridines, BPy(OH), in addition to small amounts of oxygen atoms, O(3P). Molecular oxygen quenches 3BPyO*, kQ = 1.4 × 109 M-1 s-1, but the yields of O(3P) increase in O2-saturated solutions to 36%. Other triplet quenchers have a similar effect, which rules out the observed 3BPyO* as a source of O(3P). It is concluded that O(3P) is produced from either 1BPyO* or a short-lived, unobserved, higher energy triplet generated directly from 1BPyO*. 3BPyO* is reduced by Fe2+ and by ABTS2- to the radical anion BPyO.- which exhibits a maximum at 510 nm, ε = 2200 M-1 cm-1. The anion engages in back electron transfer with ABTS.- with k = 1.7 × 109 M-1 s-1. The same species can be generated by reducing ground state BPyO with .C(CH3)2OH. The photochemistry of BPyO in acetonitrile is similar to that in aqueous solutions.
 [1] ;  [1]
  1. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
IS--J 8304
Journal ID: ISSN 1463-9076
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 16; Journal Issue: 36
Royal Society of Chemistry
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States