LASER APPLICATIONS IN CHEMISTRY AND BIOLOGY - STIMULATION, OBSERVATION, AND MANIPULATION

Results from three different types of laser-based experiments are pres ented. Using translationally-excited H atoms, the reaction dynamics of H(2S) + O2(3SIGMA(g)-) --> OH(2PI) + O(3P) was investigated. In order to study the influence: of selective reagent translational excitation on t-he reactivity, absolute reaction cross sections and nascent OH p roduct quantum-state distributions were measured at different collisio n energies by means of the laser photolysis/laser-induced fluorescence (LP/LIF) ''pump-probe'' technique. The measured absolute reaction cro ss sections: sigma(R)(1.0 eV) = (0.20 +/- 0.08) angstrom2, sigma(R) (1 .6 eV) = (0.58 +/- 0.17) angstrom2, and sigma(R)(1.9 eV) = (0.35 +/- 6 .14) angstrom2 clearly confirm the presence of a pronounced maximum in the excitation function (Kessler, K.; Kleinermanns, K. J. Chem. Phys. 1992,97: 374). The experimental results are compared with results fro m quasiclassical and recent 3D quantum scattering calculations on ab i nitio potential energy surfaces. In addition, results from experiments are reported in which two-dimensional laser light sheet techniques we re applied to investigate both the NO formation in a domestic natural gas burner and fuel mixing processes in combustion engines. Images of temperature and NO concentration distributions, as well as series of i mages of the fuel distribution, are presented. Finally, recent results of laser applications in biology are reported. A new concept in biodi agnostics using multiplex dyes, which have different characteristic fl uorescence lifetimes but identical excitation and emission spectra, to distinguish different biomolecules has been developed. First experime nts are described in which multiplex dyes in capillaries were identifi ed by steady-state fluorescence spectroscopy using a diode laser syste m. In combination with a pattern recognition technique, a detection li mit of about 100 molecules per 25 picoliters detection volume was dete rmined. The possible application in DNA sequencing is discussed. Resul ts from laser-induced cell fusion experiments, in which the laser nano scalpel and photonic tweezers techniques were combined, are also prese nted.