We demonstrate evidence of selective laser-induced desorption of ground state Br(2P3/2) and spin-orbit excited state Br*(P1/2) atoms from single crystals at 6.4 eV. Laser excitation tuned selectively to a surface resonance below the first bulk absorption band excites surfaces states preferentially leading to surface specific reaction while inducing relatively insignificant bulk reaction. The experimental results are supported by embedded cluster ab initio calculations that indicate a reduced surface exciton energy compared to that of the bulk exciton with a slight further reduction for steps and kink sites. Low fluence irradiation of cleaved KBr crystals, near the calculated surface exciton energy of 6.2 eV, produces hyper-thermal Br(2P3/2) emissions without a significant thermal or Br*(2P1/2) component. The hyper-thermal emission is shown theoretically to be characteristic of surface induced reaction of exciton decomposition while thermal Br emission is attributed to bulk photoreaction.
Revised: November 15, 2001 |
Published: November 22, 2001
Citation
Hess W.P., A.G. Joly, D.P. Gerrity, K.M. Beck, P. Sushko, and A. Shluger. 2001.Selective laser desorption of ionic surfaces: resonant surface excitation of KBr.Journal of Chemical Physics 115, no. 20:9463 - 9472.PNNL-SA-34994.