Desorption
induced by electronic transitions (DIET) and its variant DIMET (M = ‘Multiple’),
are among the simplest possible “reactions
” of ad-species involving ultra-short lived electronically
excited states at surfaces. The non-adiabatic bond-cleavage can be enforced, for
example, with laser irradiation or with electrons or holes emitted from the tip of a
scanning tunnelling microscope (STM). The transient creation of excited intermediates
can proceed directly (localised to the adsorbate–substrate complex), or indirectly (i.e., through
the substrate). To understand the basic processes, simple one-mode two-state “toy
models” such as the Menzel–Gomer–Redhead (MGR) or the Antoniewicz scenarios
have proven very useful in the past. We adopt and extend MGR- and Antoniewicz-type
models together with numerically exact open-system density matrix theory
to address a few actual problems/experiments in DI(M)ET: (1) Direct, laser-induced desorption
of H(D) from Si(100) surfaces which has been realised in the continuous-wave DIET
regime only recently [T. Vondrak and X.-Y. Zhu, Phys. Re. Lett., 1999, 82, 1967], is studied and compared to so-far hypothetical femtosecond laser desorption. The possibility of controlling the reaction by shaping the laser pulses is addressed. (2)
For the same system, temperature effects are studied for electron- or hole-stimulated desorption with an STM [T. C. Shen, C. Wang, G. C. Abeln, T. R. Tucker, J. W. Lyding, Ph. Avouris and R. E. Walkup, Science, 1995, 268, 1590; C. Thirstrup, M. Sakurai, T. Nakayama and K. Stokbro, Surf. Sci., 1999, 424, L329]. A modified version of Gadzuk’s “
sudden transition and averaging” approach is adopted which accounts for temperature dependent excited state lifetimes. (3) For photodesorption of NO from Pt(111), based on
quantum dynamical simulations possible experimental tests involving static electric fields
are suggested to address the relevance of the recently challenged [F. M. Zimmermann, Surf. Sci., 1997. 390, 174],
“negative
ion resonance” model of the
Antoniewicz type.