Kinematically-complete measurements of laser-induced dissociation of C$_2$H$_2^q$*

We examine intense femtosecond laser-induced fragmentation of acetylene dications and monocations [1]. Probing these molecules as keV ion-beam targets and focusing on dissociation ensure that the dynamics occur in a single charge state. We observe both acetylene-like breakup (CH$^{q_1}$~+~CH$^{q_2}$) and vinylidene-like breakup (C$^{q_1}$~+~CH$_2^{q_2}$) of the initially linear HCCH configuration C$_2$H$_2^q$ molecules (where $q=q_1+q_2$). For the acetylene dication, the triplet electronic states play a dominant role in the CH$^+$~+~CH$^+$ channel, in contrast to previous photofragmentation studies of neutral C$_2$H$_2$ targets, e.g., [2,3], wherein the singlet states are likely the main contributors. Plausible pathways leading to CH$^+$~+~CH fragmentation of the acetylene monocation are also discussed. The dynamics underlying the vinylidene-like breakup channels are less clear and call for more complete structure calculations and better understanding of the isomerization process. \\ {[1]} B. Jochim \emph{et al.}, Phys. Rev. A \textbf{101}, 013406 (2020); {[2]} A. S. Alnaser \emph{et al.}, J. Phys. B \textbf{39}, S485 (2006); {[3]} T. Osipov \emph{et al.}, J. Phys. B \textbf{41}, 091001 (2008).