FLUORESCENCE LIFETIMES OF LASER-EXCITED ALKOXY $RADICALS^{\ast}$
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Date
1995
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Ohio State University
Abstract
Alkoxy radicals play a leading role as oxidation intermediates in the combustion of hydrocarbons and in air pollution. The radicals were generated in a supersonic expansion by photofragmentation of alkylnitrite precursors and subsequently excited by a frequency-doubled Nd: YAG-pumped dye laser. Fluorescence decay following excitation was displayed on the screen of a digital oscilloscope and stored for analysis. Fluorescence lifetime data involving the CO - stretch vibrational mode for excited vibrational quanta $\nu^{\prime} = 0-5$ for methoxy, ethoxy and isopropoxy were found to be in the range $0.15-3.00 \mus$. Of the three transient species studied, isopropoxy had the shortest lifetime, methoxy the longest, and ethoxy was intermediate between the two. For example, for two quanta excitation of CO-stretch, the lifetimes were $1.55\mus$ for methoxy, $0.98\mus$ for ethoxy and $0.62\mus$ for isopropoxy. Time-resolved emission of ethoxy for the vibronic band involving five quanta of CO-stretch excitation gave a considerably reduced lifetime of $0.14\mus$. All of the above-cited observations appear to point to the availability of important non-radiative decay channels for excited alkoxy radicals.
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$^{\ast}$Financial support from the U.S. Environmental Protection Agency's Office of Exploratory Research (# R819720-01-0), NASA Lewis Research Center (NAG3-1677) and the Center for the Study of Terrestrial and Extraterrestrial Atmospheres (NASA NAGW-2950) is gratefully acknowledged.
Author Institution: Howard University, Washington, D.C. 20059.
Author Institution: Howard University, Washington, D.C. 20059.