Photodissociation of Linear Carbon Clusters Cn (n = 4−6)

The photodissociation of mass-selected linear carbon clusters (C n, n = 4−6) is studied using fast beam photofragment translational spectroscopy. The photofragment yield (PFY) spectra consist of several continua spanning the whole visible and ultraviolet region. The product mass distributions for dissociation of C n clusters are dominated by C 3 and its partner fragment C n - 3, although some minor channels are also identified for dissociation of C 4 and C 5 clusters. Translational energy P ( E T ) distributions for the C 3 + C n - 3 channel were measured at several photolysis energies. The PFY spectra and P ( E T ) distributions indicate that multiphoton dissociation occurs at photon energies below the dissociation threshold and that both single-photon and multiphoton dissociation occur above the threshold. The one-photon components of the P ( E T ) distributions can be modeled by phase space theory (PST), suggesting that photoexcitation is followed by internal conversion to the ground state. The PST analysis yields dissociation energies for C n → C 3 + C n - 3 in reasonable agreement with recent Knudsen effusion mass spectrometry measurements.