Comparison of Fission Fragment, Pulsed Laser, and Electric Pulse Induced Molecular Desorption

Abstract

Several methods of molecular desorption using a rapid dissipation of energy near the surface are discussed. Among them fission fragments, pulsed laser beams, and short electric pulses primarily cause electronic transitions at the solid surface, and are thus discussed in more detail. However, the properties of this molecular desorption are very much independent of the detailed kind of excitation. Always, even large and fragile molecules are desorbed. The ions found in TOF mass spectrometry are even-electronic,quasimolecular and fragment species mainly, they are only a little vibrationally excited, possess a few eV kinetic energy, and are emitted mainly in the forward direction. Their chemical and physical properties do not depend on the density of dissipation, except for the number of ions produced, or on other excitation parameters,but they are very much related to the physical and chemical status of the adsorption layer before dissipation. — Microscopically a sudden perturbation excitation model, and macroscopically a far-from-equilibrium phase transition model, are given, which fit the observed data properly.