Kinetic energy distribution of H+ desorbed by core-level excitations of condensed ammonia using a miniature cylindrical mirror analyzer (CMA)

We have developed a miniature cylindrical mirror analyzer (CMA) mounted on a 70-mm-diameter conflat flange for measurements of kinetic energy distribution of ions desorbed in the polar angles of 24°-28° from the surface normal. The acceptance solid angle is 0.16 sr and the energy resolution (FWHM) is estimated as E/ΔE = 20. We have applied it for measurements of kinetic energy distributions of ions desorbed from condensed ammonia (NH3) at the surface 4a1 ← N 1s resonant transition (hν = 400.7 eV) and at N 1s ionization (hν = 412.5 eV). The results support the two H+ desorption mechanisms proposed previously, that is, a four-step mechanism involving ultrafast H2N-H extension within the lifetime of the N 1s core hole at 4a1 ←  N 1s, and a normal Auger stimulated ion desorption mechanism at N 1s ionization.