Separating the Vibrationally Resolved Auger Decay Channels for a CO Core Hole State

The $K\mathrm{\text{−}}VV$ Auger spectrum of carbon monoxide (CO) excited by C $1s$ photoionization has been investigated with a novel electron-electron coincidence setup. The energy resolution is sufficiently high to resolve the vibrational energy levels of the core-ionized intermediate state and of most dicationic final states in the two-dimensional electron energy map. We demonstrate how the influence of vibrational states on a molecular Auger spectrum can be accessed experimentally without the constraint of averaging over all intermediate state energies.

Figure 1

Photoelectron-Auger electron coincidence spectrum of CO after C $1s$ ionization at 304 eV photon energy. For each combination of ${\mathrm{CO}}^{+}$ intermediate and ${\mathrm{CO}}^{2+}$ final states the number of electron pairs recorded is plotted on a color-coded map. The contribution of random coincidences has been subtracted [21]. Intensities are given as events per unit energy and events per unit ${\mathrm{\text{energy}}}^2$, respectively.

Figure 2

Decay intensities from the C $1s^{-1}$, ${\nu }^{\prime }=0$ (symbols), ${\nu }^{\prime }=1$ (red) and ${\nu }^{\prime }=2$ (blue) intermediate states. Intensities have been summed within a 150 meV interval around the respective intensity maximum in the summed photoelectron curve (left-hand side panel of Fig. 1). Error bars shown for the ${\nu }^{\prime }=0$ curve are representative for all data. The curves for ${\nu }^{\prime }=1$ (red) and ${\nu }^{\prime }=2$ have been offset by 10 000 and $25000\mathrm{\text{events}}/\mathrm{eV}$ to improve visibility.