Desorption force on hydrogen atoms from resonant excitations of the H:Si(0 0 1)-(2 × 1) surface

Laser excitation at 7.9 eV photon energy leads to the desorption of hydrogen atoms from the H:Si(0 0 1)-(2 × 1) monohydride surface [T. Vondrak, X.-Y. Zhu, Phys. Rev. Lett. 82 (1999) 1967]. In the present paper we address the electronic excitations relevant for this desorption process and investigate the corresponding force on the hydrogen atom. The excited state is described by ab-initio many-body perturbation theory. A particular problem is posed by the resonant character of the excited state in question, leading to delocalization and fast decay. Here we suggest to employ an additional short-range confinement potential to localize the excited state on the Si-H bond which is broken in the desorption process.