Low Temperature Chemistry of Planetary Atmospheres



This NASA funded project is aimed at providing entirely new kinetic and isomer resolved product branching ratio measurements at low temperatures (80K). The operational layout of the new Laval nozzle apparatus is shown below.  A pair of pulsed valves attached to a nozzle block creates a collimated pulsed supersonic expansion.  This collimated flow travels 5-20 cm before encountering the airfoil.  Reactants and radical precursors are seeded into the flow in a balance of nitrogen.  A column of radicals is then formed by photolyzing the radical precursors using a pulsed excimer laser (193 or 248 nm).   The synchrotron beam passes within 1- 5 mm of the aperture located in the apex of the airfoil and the resulting photoions are collected using a three element extraction lens.  A mass spectrometer monitors the transient evolution of a single mass during the reaction.  By monitoring either the time evolution of a radical intermediate (e.g. CH, C2H, CH3, etc.) or the formation of a stable reaction product the kinetics of the reaction can be quantified.  Photoionization efficiency spectra, used for isomer identification, are obtained by scanning the photon energy of the synchrotron and recording the ion signal for a selected mass.