Probing dissociative molecular dications by mapping vibrational wave functions

Abstract

We present high-resolution photoelectron-Auger-electron coincidence spectra of methane (CH 4 ). Since the vibrational structure in the photoelectron spectrum is resolved, the Auger spectra corresponding to different vibrational levels can be separated. The seven final states of CH 2+ 4 are either dissociative or metastable, but in any case are populated in a repulsive part of their potential-energy curve via the Auger decay. The Auger line shapes can therefore be obtained by mapping the vibrational wave functions of the core-hole state into energy space. We have implemented this connection in the data analysis. By simultaneously fitting the different Auger spectra, detailed information on the energies of the dicationic states and their repulsive potential-energy curves is derived.

Conformational and nuclear dynamics effects in molecular Auger spectra: fluorine core-hole decay in CF4

“…In our experiment, the exact energy of the intermediate state for every Auger electron was observed by photoelectron-Auger electron coincidence spectroscopy with high energy resolution, as developed by some of the present authors [6,7,8] and by others [9,10]. At fixed photon energy, our measurements show a dependence of the Auger spectrum on the exact kinetic energy of the emitted photoelectron.…”

“…For bound-to-metastable transitions as observed in small molecules, such as CO, the Franck-Condon factors can lead to a variety of complex structures in this plane [4,6,7]. In methane, representing the case of a transition from a bound intermediate to a set of unbound final states, the coincident spectrum appears mostly to be arranged along the lines of constant intermediate state energy [8]; these lines correspond to the v ′ = 0 and v ′ = 1 core ionized states and would be horizontal in the present figure. On the other hand, the present coincidence spectrum of CF 4 is mostly structured along vertical lines, i.e.…”

Simulation of Auger decay dynamics in the hard X-ray regime: HCl as a showcase

“…The approximation of the Airy functions with δ functions allows also a derivation of the Franck-Condon factors for higher vibrational states in the bound potential, see e.g. 21 .…”

The O K−2V spectrum of CO: the influence of the second core-hole

“…According to the Condon reflection approximation, 60 the slope of the PEC will depend on the full width at half maximum (FWHM) of the Gaussian profile describing the line-shape of the recorded transition, through S = as, as has been demonstrated in ref. 61, where S is the slope of the potential energy curve, s the FWHM of the Gaussian and a 2 = mo/h , with m being the reduced mass of the molecule and o its vibrational frequency in the electronic ground state. The line-shape of the transition will formally be described by a Voigt profile, being the result of the convolution of a Lorentzian profile accounting for the lifetime broadening, with a Gaussian profile having two contributions.…”