The reaction pathways and intermediates for HCCH oxidation and linear carbon cluster formation are characterized by the technique of fast-beam radical photofragment spectroscopy. A systematic study of HCCO, CCO and excited singlet state CCO radicals has identified new in situ probes and significantly refined the heats of formation for these species. This allows definition of a new reaction pathway for HCCH oxidation, which proceeds via HCCO and CCO to CO and electronically excited CO. Results are also presented on the photodisssociation of mass-selected linear-carbon clusters, i.e. lin-C4, C5 and C6, yielding their bond dissociation energies,heats of formation, unimolecular dissociation behaviors and product branching ratios. This information identifies a reaction pathway for linear carbon chain formation to be C2 addition of only odd carbon clusters.