Double-photoionization of CO few eV above threshold

A. Belkacem, T. Osipov, M. Hertlein, M. Prior, H. Adaniya, B. Feinberg
( Lawrence Berkeley National Laboratory)

Th. Weber, T. Jahnke, R. Dorner, L. Schmidt, M. Schoffler, O. Jagutzki
( University of Frankfurt)

C.L. Cocke
( Kansas State Universiy)

A. Landers
( U. of Auburn)

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.

This work was supported by the Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Submitted to DAMOP, May 2006 in Knoxville, TN.

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