Electronic state dependence in the dissociation of core-ionized methane

Abstract

Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron-ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a −2 1 and 2a −1 1 1t −1 2 states, interpreted as an 'excess-energy-dependent' concerted dissociation process for the 2a −2 1 state and an 'electronic-state-dependent' sequential process for the 2a −1 1 1t −1 2 state.

Probing dissociative molecular dications by mapping vibrational wave functions

“…The same is true for the ADC(2) work of Tarantelli et al [39], although in absolute energy there is a discrepancy of 2.5 eV. In one of the experimental papers, relative state energies were derived from Auger decay, without, however, resolving the Auger spectra due to the different vibrational states [22]. The results of this latter work do not agree with ours, for reasons that are not understood at present.…”

“…The dicationic states of this molecule, in particular the ground state, have attracted considerable interest. Methods for their investigation include Auger decay [13,14], charge stripping spectroscopy (see the critical review in [15]), double charge transfer [16][17][18], photoelectron-ion-ion coincidence spectroscopy [19], photoelectron-photoelectron coincidence spectroscopy [20], coincidence spectroscopy of Auger electrons and ions [21][22][23], and quantum chemical calculations [15,[23][24][25][26]. The four lowest dicationic states actually possess a potential-energy surface with a local minimum [23], i.e., CH 2+ 4 can be metastable.…”

Probing the dynamics of dissociation of methane following core ionization using three-dimensional molecular-frame photoelectron angular distributions

“…Such measurements are sometimes called recoil-frame photoelectron angular distributions (RFPADs) to distinguish them from the full MFPAD for the completely oriented molecule. These decay channels and many others have been studied before in experiments that observe the Auger electron in coincidence with the ionic fragments [10][11][12]. In this study we build particularly on the previous work of Kukk et al [10] The central question that determines if coincidence measurements in these channels yield information on the orientation of the molecule is whether or not the dissociation dynamics are prompt and the fragmentation occurs essentially along the directions of the bonds in the molecule.…”

“…These decay channels and many others have been studied before in experiments that observe the Auger electron in coincidence with the ionic fragments [10][11][12]. In this study we build particularly on the previous work of Kukk et al [10] The central question that determines if coincidence measurements in these channels yield information on the orientation of the molecule is whether or not the dissociation dynamics are prompt and the fragmentation occurs essentially along the directions of the bonds in the molecule. This condition, called 'axial recoil' for diatomics may or may not be satisfied because the molecule can rotate before dissociating in some cases [13].…”

“…That comparison leaves little doubt that the RFPADs measured in this channel are consistent with axial recoil and with the MFPADs measured in the [H + , H + , CH 0 2 ] channel discussed earlier. ++ 4 The RFPADs observed in the breakup leading to [CH Our point of departure is a result of Kukk et al [10]. By measuring the energies of Auger electrons in coincidence with the ionic fragments, these investigators were able to give compelling evidence in 2007 that the the CH in tetrahedral geometry and that the same state produces CD + 3 from dissociation of CD ++ 4 .…”