Double-photoionization of CO few eV above threshold

We measured double photoionization of CO molecules at 48 eV photon energy. The double ionization of CO produces mostly C$^{+}$ + O$^{+}$ fragments with non-measurable amounts of CO$^{2+}$. The formation of C$^{+}$ + O$^{+}$ can proceed through two possible channels: a) Direct ionization of two electron into the continuum -- similar to the H2 double ionization -- direct channel. b) Ionization of one electron into the continuum followed by autoionization of a second electron -- Indirect channel. The electron distribution measured with a COLTRIMS shows a very clear distinction of the direct and indirect channels. The kinetic energy release spectrum shows a series of peaks corresponding to the transient vibrational states of the various electronic states of (CO$^{2+})$*. These states are similar to previous measurements at higher energies (K-shell photoionization). (CO$^{2+})$* is found to predissociate through a $^{3}\Sigma ^{-}$ and $^{1}\Delta $ dissociative states leading to considerably faster dissociation times than natural lifetimes of the electronic bound states.