J. Phys. Colloques
Volume 49, Numéro C6, Novembre 198835th International Field Emission Symposium / 35éme Symposium International d'Emission de Champ
|Page(s)||C6-209 - C6-214|
J. Phys. Colloques 49 (1988) C6-209-C6-214
THE EFFECTS OF VIBRATIONAL AND ROTATIONAL MOTION ON THE FIELD DISSOCIATION BY ATOMIC TUNNELING OF HeRh2 IONSN.M. MISKOVSKY et T.T. TSONG
Physics Department, The Pennsylvania State University, University Park, Pennsylvania, PA 16802, U.S.A.
When a compound ion is placed in an intense electric field, the potential barrier may be lowered to the extent that dissociation can occur via quantum mechanical tunneling (1). We have made a numerical study of the detailed atomic process of dissociation. When the molecular ion, HeRh2+, is field evaporated from the surface, it cannot dissociate since it is in the wrong orientation. As the molecular ion rotates and vibrates, the probability of dissociation becomes non-zero when the angle of rotation lies in the range 90° < θ < 270°. The model calculations predict the existence of a field dissociation zone of width 124 Å with the peak in the dissociation located at 197 Å above the surface. These results are in excellent agreement with the experimental data of Tsong and Liou (2,3). In addition, the model calculations predict four dissociation peaks within this zone due to the vibrational motion of the ion. These fine structure lines in the secondary Rh2+ peak are separated on the average by 0.86x10-13 sec, implying an average vibrational frequency of 1.2x1012 Hz. Their relative intensities are 0.356, 1.00, 0.784, and 0.235. These fine structure lines in the secondary Rh2+ peak should be experimentally observable provided the stability and the resolution of the atom-probe are further improved by a factor of about five. We are in the process of making an improvement so that the vibrational features in the field dissociation can be directly observed in the time-of-flight spectrum.