Electron beam induced damage of NaNO3 single crystals: An energy, temperature, and quantum state resolved study

Electron beam induced damage of NaNO3 single crystals is examined using laser resonance enhanced multiphoton ionization detection of the neutral desorption products, post-irradiation temperature-programmed desorption (TPD), secondary electron emission microscopy (SEEM), and Auger electron spectroscopy (AES). The damage initially involves destruction of the nitrate group and production of O (P-3(J)) and NO ((2)Pi) fragments with nonthermal energy distributions. Specifically, the O (P-3(J)) J State distribution measured at 100 eV incident electron energy is 5:1.5:0.25 for J = 2:1:0, the NO ((2)Pi) vibrational state distribution is 1:0.56:0.35:0.40:0.23 for nu = 0:1:2:3:4, and the NO ((2)Pi(1/2,3/2)) rotational distribution has a high population of the upper ((2)Pi(3/2)) spin-orbit component. Production and desorption of these nonthermal fragments are dominated by the decay of {NO3-}*. At higher electron fluences, thermalized NO, O-2, and NO2 are also produced and released, though the NO2 is a minor product. We suggest that the formation and desorption of thermalized NO and O-2 both involve NO2- defect states and unimolecular dissociation of NO3*. This is supported by the observation that the NO and O-2 yields have the same temperature dependence which is well described by the sum of two Maxwell-Boltzmann type equations with activation energies of 0.16 +/- 0.03 and 0.010 +/- 0.004 eV. O-2 gas is also released in post-irradiation thermal cycling from 110 to 440 K with peaks at similar to 260 and similar to 340 K. We associate the post-irradiation TPD of O-2 With reactions involving O atoms released during thermal decomposition of (NO2-... O) and ONOO-. The SEEM image shows damage features, and the AES spectra indicate that the irradiated region is depleted in both nitrogen and oxygen relative to Na. The elemental composition shows Na2O as a final product of the NaNO3 radiation decomposition. The 100 eV electron beam damage cross section is at least similar to 10(-16) cm(2).