Photodissociation of Linear Carbon Clusters C n (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 C3 and its partner fragment C n - 3, although some minor channels are also identified for dissociation of C4 and C5 clusters. Translational energy P(E T) distributions for the C3 + 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 → C3 + C n - 3 in reasonable agreement with recent Knudsen effusion mass spectrometry measurements.