Exploring three-body fragmentation of acetylene trication.

The three-body breakup of [CH] formed in collision with Xe moving at 0.5 atomic units of velocity is studied by using recoil ion momentum spectroscopy. Three-body breakup channels leading to (H, C, CH) and (H, H, C ) fragments are observed in the experiment and their kinetic energy release is measured. The breakup into (H, C, CH) occurs via concerted and sequential modes, whereas the breakup into (H, H, C ) shows only the concerted mode. By collecting events coming exclusively from the sequential breakup leading to (H, C, CH), we have determined the kinetic energy release for the unimolecular fragmentation of the molecular intermediate, [CH]. By using ab initio calculations, the potential energy surface for the lowest electronic state of [CH] is generated, which shows the existence of a metastable state with two possible dissociation pathways. A discussion on the agreement between our experimental results and these ab initio calculations is presented.