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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, λ max 490 and 380 nm. 3BPyO* decays with the rate law k decay/s -1 = (3.3 ± 0.9) × 10 4 + (1.5 ± 0.2) × 10 9 [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*, k Q = 1.4 × 10 9 M -1 s -1, but the yields of O( 3P) increase in O 2-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 Fe 2+ and by ABTS 2- 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 bymore » reducing ground state BPyO with .C(CH 3) 2OH. The photochemistry of BPyO in acetonitrile is similar to that in aqueous solutions.« less
Authors:
 [1] ;  [1]
  1. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
Publication Date:
OSTI Identifier:
1149365
Report Number(s):
IS-J 8304
Journal ID: ISSN 1463-9076
DOE Contract Number:
AC02-07CH11358
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 16; Journal Issue: 36
Publisher:
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
Language:
English
Subject:
36 MATERIALS SCIENCE