Kinetics of radicals in aqueous phase
Laser-based studies of atmospheric radical reactions in aqueous solution are a major activity in the laboratory. These reactions are of importance for chemical processes in haze particles, fog, rain and clouds. In order to understand oxidation processes of organic compounds (alcohols, carbonyls, acids, aromatics) within the tropospheric multiphase system reactions of OH, NO3, SOX- and halogen radicals are characterized as a function of temperature, pH, oxygen content and ionic strength. Measurements were done with a laser flash photolysis long path absorption (LFP-LPA) setup (Figure 1). Kinetic studies were done directly or using competition kinetic applying a pulsed (excimer) and different continuous wave lasers (Argon ion laser, diode laser, He-Ne-laser, He-Cd-laser). The experimental set-up consists of a multi gas excimer laser (Kr/F - λ = 248 nm, Xe/Cl - λ = 308 nm or Xe/F - λ = 351 nm), which has a pulse length of 10 - 40 ns. Analytical light sources are both continuous wave lasers and lamps. In order to increase the optical path length of the analytical light through the reaction cell two mirrors in White configuration are used (Figure 2 and 3). Detectors applied are photodiodes, photomultiplier, diode arrays and CCD-cameras. Therefore, experimental set-ups can be used for both kinetic studies and spectroscopic studies of short-lived transient species (e.g., organic peroxy radicals).