Laboratory Measurements of Fast Hydrogen (H) and Oxygen (O) Atom Collisions Relevant to the Upper Atmosphere

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Fast hydrogen, nitrogen, and oxygen atoms in the energy range 1-100 eV and higher are produced in the earth's upper atmosphere through phenomena such as photodissociation, radiative recombination, dissociative recombination, dissociative attachment, charge exchange, and superelastic (quenching) collisions. Many of these phenomena are induced by lightning discharges, which are responsible for emissions known as elves, red sprites, and blue jets. The fast atoms collide with species such as N2, O2, NO, H2O, CO2, etc. to produce, either through chemical reaction or direct excitation of the target, emissions in the upper atmosphere and thermosphere such as the hydrogen nighttime and polar-cusp aurora, and the hot oxygen corona and geocorona. Using a unique experimental facility at JPL, constructed with prior NSF support, fast ground-state hydrogen and oxygen atoms will be generated in the laboratory energy range 2-100 eV. The fast atoms will be used to study two classes of atmospheric reactions with the important species N2, O2, and NO. These classes are (a) infrared (vibrational) excitation and emission, where cross sections are measured using an integrating sphere coupled to a HgCdTe infrared detector; and (b) electron-capture and stripping, where cross-section and mass/charge ratio measurements are made using a Penning ion trap.