Phase coherence in atomic vibration in field dissociation of field desorbed diatomic ions

In an applied electric field of a few volts per angstrom, diatomic ions can dissociate into atomic ions and neutral atoms by atomic tunneling. The dissociation rate has been found to depend on the field strength and the orientation of the ion with respect to the field. We report here an observation, by pulsed-laser-stimulated field desorption and high-resolution time-of-flight spectroscopy, of the atomic vibrational features in field dissociations of a gas ion D2+ and a metal compound ion 4HeRh2+. The vibrational effect produces secondary peaks in the ion kinetic-energy distributions of D+ and Rh2+. From this observation we conclude that D2+ and 4HeRh2+ ions are field desorbed from the emitter surfaces coherently with respect to their atomic vibrational phases. Some related coupling constants, as well as the dissociation probability of these compound ions, which is based on a WKB approximation of the barrier penetration probability, are presented and compared with the experimental results