Dissociation of van der Waals Complexes in High Rydberg States Induced by Electric Fields

Abstract

Due to its mass and energy selectivity, mass-analyzed threshold ionization spectroscopy provides information on the energetic position of the dissociation threshold of van der Waals complex cations. In this work we report the first observation of a shift of the dissociation threshold of van der Waals complexes in high Rydberg states induced by an applied electric field of several hundred V/cm. The detection of a ≈70 cm-1 shift is possible for fluorobenzene·Ar because of its high density of optically accessible vibrational states around the dissociation threshold at 568 cm-1. This shift is explained by a field-induced coupling between high and low Rydberg states of different series.

Binding energies and dissociation pathways in the aniline-Ar2 cation complex

“…Below 480 cm −1 there are three bands which show intensity in both the complex and monomer channels, with the monomer increasing in intensity relative to the complex for each band. The presence of intensity in the monomer channel just below the actual threshold has been documented and explained by Gretner et al 25 as being due to coupling to lower Rydberg states that occurs when large voltage extraction pulses are used, such as the ϳ900 V / cm employed in our experiment. The threshold for disappearance of the complex signal is not affected by the field and thus is used as a more reliable value to determine the dissociation energy.…”

“…The broadening could be due to the Rydberg coupling mechanism mentioned above. 25 The threshold for loss of the second Ar occurs within the profile of a strong band and so one might expect a sharp threshold. However, this is not observed and is likely due to the fact that the loss of the first Ar can take place with varying degrees of kinetic energy loss, therefore the remaining products have a distribution of internal energy.…”

Chemical Applications of Zero Kinetic Energy (ZEKE) Photoelectron Spectroscopy

“…An experiment by Krause and Neusser [138,139] gave the following results for the dissociation of the C 6 H 6 ± Ar van der Waals complex (the frequency of the first laser was tuned to the intermediate state of the C 6 H 6 ± Ar complex produced in the seeded supersonic jet): The 6 1 0 transition is red-shifted by 21 cm À1 from the corresponding transition in benzene. Under these conditions the selectivity of excitation of the intermediate state is very good, and it is possible to ionize only the C 6 H 6 ± Ar complex.…”

Anwendungen der Zero-Kinetic-Energy(ZEKE)-Photoelektronenspektroskopie in der Chemie

“…Ein Beispiel dafür ist die Dissoziation des Benzol-Argon-van-der-Waals-Komplexes. Ein Experiment von Krause und Neusser et al [138,139] ergab hierbei folgende Resultate (die Frequenz des ersten Lasers wurde auf den Zwischenzustand des in einem Überschallmolekularstrahl erzeugten Benzol-Argon-Komplexes eingestellt): Der 6 1 0 -Übergang ist gegenüber dem entsprechenden Übergang im Benzol um 21 cm À1 zu niedrigerer Energie hin verschoben. Unter diesen Bedingungen ist die Selektivität der Anregung des Zwischenzustands sehr gut; damit ist eine ausschlieûliche Ionisation des Benzol-Argon-Komplexes möglich.…”