Vibronic coupling in the K shell excitation of ethyne

Dynamics of proton migration and dissociation in core-excited ethyne probed by multiple ion momentum imaging

“…13 The ground state of the ethyne molecule is linear with D ϱh symmetry, but the C 1s −1 ‫1ء‬ core-excited state has a bent equilibrium geometry. 14 The absorption spectrum near the C 1s edge also shows evidence of excited bending modes 15 and Adachi recently used photoelectron-ion-ion coincidences to show the role of core-hole localization in bond breaking. 16 The recent study by Kimberg et al 17 made the connection between the core-excited state and the alignment of bonds in the final dicationic state, and they described the role of the core-hole lifetime and the transition dipole moment in detail.…”

Unambiguous observation of F-atom core-hole localization in CF4 through body-frame photoelectron angular distributions

“…Symmetric ionic states arising from the removal of an electron from a core orbital in symmetryequivalent atoms have energies that can lie entirely or partly within their Auger decay widths and are effectively degenerate. The 2 A 1 and 2 T 2 states of CF 4 + with a fluorine K-shell vacancy in this study are examples of such states, and there are numerous other examples previously investigated by Auger spectroscopy [1][2][3][4]. For more than four decades, experimental and theoretical studies have been directed toward understanding how combinations of such states break molecular symmetry and the role they play in molecular dynamics and spectroscopy.…”

“…Consequently, the vibrational structures in the C(1s −1 ) → π * bands in both acetylene [3] and ethylene [4] are well described by a theoretical treatment of vibronic coupling in both the core and valence orbital spaces with broken-symmetry orbitals. The signature of core-hole localization can in principle also be observed in dynamical processes such as core-level photoionization, when viewed in the body frame.…”

“…Observing the photoejected electron in coincidence with an F + atomic ion after Auger decay is shown to select the dissociation path where the core hole was localized almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling CF 3 + and F + atoms elucidates the underlying physics that derives from the Ne-like valence structure of the F(1s −1 ) core-excited atom.…”

“…In order to detect the electrons of interest with a full solid angle, static magnetic fields of 8.2 and 4.2 G parallel to the momentum spectrometer time-of-flight axis were employed in both investigations. In each experiment the photoelectron was recorded in coincidence with a CF 3 + and F + ion on a shot-by-shot basis and for known orientations of the linear polarized light. Other details of the experimental setup were the same as those in an earlier COLTRIMS study of carbon K-shell ionization in CF 4 [15].…”