Photodesorption of excited iodine atoms from KI (100).

ABSTRACT

Band-to-band photoexcitation of potassium iodide single crystals with UV photons produces thermal and hyperthermal I-atom emission in both the ground I((2)P(3/2)) and spin-orbit excited I( *)((2)P(1/2)) states. Thermal halogen atom emission is preceded by H-center diffusion from bulk to surface and excited atom emission indicates that the excited hole spin state relaxation is incomplete before H-center diffusion to the surface. The hyperthermal I-atom kinetic energy distribution is inverted in the sense that the electronically excited I( *)((2)P(1/2)) atoms are more energetic than the ground state I((2)P(3/2)) atoms. The mechanism for hyperthermal emission of halogen atoms and their kinetic energy distributions are discussed in terms of recent calculations and a simple curve crossing model for the dynamical desorption process.