Observation of collisional ionization electron spectra of van der Waals clusters with metastable He*(2 3S) atoms: An evidence for autoionization from superexcited Ar clusters

Abstract

Penning ionization electron spectra (PIES) of van der Waals clusters have been observed for the first time by means of a newly developed magnetic bottle electron spectrometer, which is 1000 times more efficient than a conventional PIES apparatus. In the PIES of Ar clusters with He*(2 3S), two bands of Ar 3p hole characters with different ionization energies (IE), band A (IE=ca.15 eV) and band B (IE=ca.13.5 eV), were observed. Band A was assigned to vertical transitions in Franck–Condon regions corresponding to the band in the ultraviolet photoelectron spectra (UPS) of clusters reported by Carnovale et al. [J. Chem. Phys. 90, 1452 (1989)]. Band B, which is an extra band missing in the UPS of clusters, can be ascribed to the autoionization into a stable structure of Arn+ via superexcited states of Arn. Band B can be considered as an adiabatic ionization which is forbidden as a direct ionization. The energy difference of ca. 1.5 eV between the vertical IE for band A and the adiabatic IE for band B was found to agree well with the reported binding energy of the trimer ion core.

Penning Ionization of Acene Molecules by Helium Nanodroplets

“…15 This method, which has been developed for many decades, has its merits for its sensitivity to the spatial electron distribution of molecules, clusters, and surfaces, and to anisotropic interaction potentials of the colliding reaction partners. 16 Besides, Penning ionization experiments involving clusters can reveal additional details of complex ionization mechanisms such as autoionization of superexcited states 16,17 and diabatic relaxation of excitation. 7,18 Traditionally, a rare gas atom, most often He due to its extremely high excitation energy, is prepared in an excited metastable state and collides with another atom, molecule, or surface, M, to induces the ionization of the latter in the reaction…”

“…This method, which has been developed for many decades, has its merits for its sensitivity to the spatial electron distribution of molecules, clusters, and surfaces and to anisotropic interaction potentials of the colliding reaction partners . Besides, Penning ionization experiments involving clusters can reveal additional details of complex ionization mechanisms such as autoionization of superexcited states , and vibronic relaxation of excitation. , Traditionally, a rare gas atom, most often He, due to its extremely high excitation energy, is prepared in an excited metastable state and collides with another atom, molecule, or surface, M, to induce the ionization of the latter in the reaction In this reaction, the excess energy is transferred to the emitted Penning electron e – . Here, E * is the energy of the metastable rare gas atom, E i is the ionization energy of the colliding particle M, and Δ E is a small energy difference between potential energy curves of the incoming He* + M and outgoing He + M + + e – channels .…”

Charge Localization in Collision-Induced Multiple Ionization of van der Waals Clusters with Highly Charged Ions

“…Such high charge states have neither been observed in fission of multiply charged van der Waals clusters nor in ion-induced fragmentation of fullerenes or metal clusters. This hints at fundamentally different excitation and fragmentation dynamics.Fragmentation and ionization dynamics of atomic and molecular van der Waals (VdW) clusters upon interaction with a variety of particles, for instance, electrons, photons, and metastable He atoms, have been investigated [1][2][3][4]. Multiply charged clusters can be efficiently prepared by core level excitation using soft x rays [4,5], multiple outer shell ionization by femtosecond laser radiation [5 -8], or electron impact [1].…”