Photodissociation of bromoacetyl bromide by using cavity ring down spectroscopy
Date Issued
2012
Date
2012
Author(s)
Fan, He
Abstract
Cavity ring-down spectroscopy (CRDS) is a high sensitivity spectral absorption technique, which is based on measurement of the decay rate of a pulsed light trapped in an optical cavity containing a pair of highly reflective (R>99.9%) mirrors. The plot of decay rate as a function of laser wavelength gives the absorption spectrum.
We use an eximer laser (248 nm) to photolyze bromoacetyl bromide, and then detect Br2 absorption transition (B3Π+0u←X1Σ+g) from elimination channel products by using CRDS. Energy and pressure dependence measurements are used to prove the Br2 elimination involving one photon dissociation process. Combining the experimental data and spectral simulation, we can obtain the branching ratio of Br2 vibrational levels which is V0:V1:V2=1:(0.5±0.2):(0.2±0.1). It means the Br2 fragments we observed is vibrationally hot. We measure the aborsorption cross-section in gas phase by using UV-Vis spectrometer, and the quantum yield is determined to be 0.24 ± 0.08 for the Br2 elimination channel of bromoacetyl bromide. We also determine the lifetime in excited state by using Laser-induced fluorescence (LIF) technique, and the radiative lifetime is approximately 150 ns. To realize self-quenching , a Stern-Volmer plot is obtained.
Subjects
CRDS
photodissociation
molecular dynamics
bromoacetyl bromide
Type
thesis
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