title: Time-resolved detection of the CF3 photofragment using chirped QCL radiation.
abstract: This paper demonstrates how a quantum cascade laser (QCL) in its intrapulse mode can provide a simple method for probing the products of a photolysis event. The system studied is the 266 nm photodissociation of CF3I with the CF3 fragments subsequently detected using radiation at approximately 1253 cm(-1) generated by a pulsed QCL. The tuning range provided by the frequency down-chirp of the QCL operated in its intrapulse mode allows a approximately 1 cm(-1) segment of the CF3 nu3 band to be measured following each photolysis laser pulse. Identification of features within this spectral region allows the CF3 ( v = 0) number density to be calculated as a function of pump-probe delay, and consequently the processes which populate and deplete this quantum state may be examined. Rate constants for the population cascade from higher vibrational levels into the v = 0 state, k 1, and for the recombination of the CF3 radicals to form C2F6, k2, are measured. The returned values of k1 = (2.3 +/- 0.34) x 10(-12) cm(3) molecule(-1) s(-1) and k2 = (3.9 +/- 0.34) x 10(-12) cm(3) molecule(-1) s(-1) are found to be in good agreement with reported literature values.
authors.affiliation: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, The University of Oxford, South Parks Road, Oxford OX13QZ, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Hancock
authors.forename: S J
authors.initials: SJ
authors.lastname: Horrocks
authors.forename: G A D
authors.initials: GA
authors.lastname: Ritchie
authors.forename: J H van
authors.initials: JH
authors.lastname: Helden
authors.forename: R J
authors.initials: RJ
authors.lastname: Walker