Coulomb explosion imaging of carbon monoxide dimers

Carbon monoxide dimers (CO)₂ have been studied since the 90’s using photon spectroscopy. However, the interpretation of the measured rovibrational spectra has shown the possible contribution of two distinct isomers of the dimer with very little binding energy difference. Our goal was to try to determine their geometry using a Coulomb explosion technique.

On the other hand, doubly charged diatomic ions have unusual properties leading to a wide range of lifetimes against dissociation. Their stability depends on both decay mechanisms and populated rovibronic levels with respect to the barrier height. Among the large variety of doubly charged diatomic species investigated so far, CO²⁺ is probably the one that has attracted the largest interest, with measured lifetimes ranging from submicroseconds to a few seconds.

We will report on experimental results obtained from collisions of slow highly charged Ar⁹⁺ ions with a carbon monoxide dimer (CO)₂ target. A COLTRIMS setup and a Coulomb explosion imaging approach are used to reconstruct the structure of the CO dimers as well as its fragmentation dynamics. The three dimensional structure is deduced from the 2-body and 3-body dissociation channels from which both the intermolecular bond length and the relative orientation of the two molecules are determined. We will show how the lifetime of metastable states of the CO²⁺ dication affects the dimer fragmentation dynamics and thus giving access to its measurement.