NEUTRAL ATOM AND MOLECULE EMISSION ACCOMPANYING 248-NM LASER IRRADIATION OF SINGLE-CRYSTAL NANO3

We report quadrupole mass-selected measurements of neutral emissions produced by exposing single crystal sodium nitrate to 248-nm radiation from a pulsed excimer laser. The intensity and identity of the observed products are a strong function of laser fluence as well as previous exposure. In particular, a strong incubation effect is observed, with weak emission intensities during the early stages of irradiation which grow dramatically with continued irradiation. At low fluences (< 80 mJ/cm(2) on laser-damaged surfaces), NO is the only neutral product observed. Thus it appears that defects created by NO emission on more or less perfect NaNO3 surfaces strongly enhance subsequent emission. At higher fluences (> 100 mJ/cm(2) on laser-damaged surfaces), a visible fluorescent plume is observed and other neutral products (primarily O-2 and Na) are emitted along with NO. Time-of-flight measurements of the anion-derived species (NO, O-2, NO2) show unusually long emission tails which are inconsistent with emission during the laser pulse only. We attribute this ''delayed'' emission to dissociative electron attachment due to charge transport from the bulk to the surface similar to electron beam induced emission.