Selective laser desorption of ionic surfaces: Resonant surface excitation of KBr

Abstract

We demonstrate evidence of selective laser-induced desorption of ground state Br(2P3/2) and spin–orbit excited state Br(2P1/2) atoms from KBr single crystals following 6.4 eV irradiation. Laser excitation tuned selectively to a surface resonance below the first bulk absorption band excites surface states preferentially leading to surface specific reactions 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 hyperthermal Br(2P3/2) emission without a significant thermal or Br(2P1/2) component. The hyperthermal emission is shown theoretically to be characteristic of surface induced reaction of exciton decomposition while thermal emission is attributed to bulk photoreaction.

Surface three-dimensional velocity map imaging: A new technique for the study of photodesorption dynamics

“…13 We chose this system as a test case for the technique since it had been previously studied by other methods. 14,15 By using a combination of TOF and VMI techniques, we were able to obtain three-dimensional velocity map images of desorbing Br and Br ‫ء‬ , that is the desorption probability, P, as a function of three Cartesian components ͑v x , v y , and v z ͒ of the velocity vector, v ជ. Our measured velocity and angular distributions are qualitatively similar to the previous work on this system but revealed new features of the desorption dynamics.…”

“…It is also interesting to compare these results to those obtained by Hess et al 14 In contrast to our results, those experiments did not show bimodal or multiple component velocity or energy distributions from desorption with 193 nm ͑6.4 eV͒ photons. At present we cannot explain the reason for the difference but it may be related to differences in the angular acceptance of the detectors used in the two experiments or to other aspects of the setup.…”

Photodesorption of Alkali Anions from Alkali-Halide Cluster Anions

“…AAP can also be seen in data from earlier studies conducted in this laboratory on sodium-chloride clusters, including NaCl n Na ÿ (n 4, 8,9,11,13,16,17,19) [23]. It appears that AAP is a nearly universal process in two-excess-electron AHCs.…”

Electronic energy transfer on CaO surfaces

“…Hyperthermal atomic desorption is taken to be a signature of surface excited state dynamics. 19 To obtain surface-specific data on the mechanisms of radiation processes in CaO thin films, we measured the relative O-atom yield and time-of-flight spectra over the energy range from 3.75 to 5.4 eV. Figure 2 shows the relative O-atom yield as a function of photon energy.…”