Spectroscopic studies for state-to-state reaction dynamics

• Main Author: Maitland, G.
• Published: University of Edinburgh 1994
• Subjects: 543.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657225

A series of experiments was undertaken to establish the spectroscopic basis of subsequent dynamical studies of elementary bimolecular reactions in the gas phase, in which laser methods are used both for the preparation of reagents and the state-specific detection of products. An apparatus was constructed which allowed gas phase molecules to be detected spectroscopically at very low densities in a state-specific fashion by either laser-induced fluorescence (LIF) or resonance-enhanced multiphoton ionization (REMPI). In REMPI experiments, further species discrimination was achieved by time-of-flight detection of the ions produced. An attempt was made to investigate the dynamics of reactions of the type Cl(<SUP>2</SUP>P) + HX (where X=Br, I) by combining REMPI detection of the products with laser photolytic production of the Cl(<SUP>2</SUP>P) atoms. It was successfully demonstrated, by direct REMPI detection, that Cl(<SUP>2</SUP>P) atoms were produced with an anisotropic spatial distribution. Due to heterogeneous reactions occurring on the surfaces of the inlets necessary to introduce the reagent precursor gases, it was, however, not possible to unambiguously identify any nascent HCl product molecules. Some preliminary measurements were also made of coherent anti-Stokes Raman spectroscopy (CARS) of HCl, with the intention of establishing the viability of the intimately related stimulated Raman pumping process for the state-selective preparation of molecular reagents in dynamical studies. In particular, the polarization properties of different spectroscopic branches were examined, allowing the feasibility of the preparation of a spatially anisotropic sample to be assessed.