A mass spectroscopic study of laser vaporized graphite in H2 and D2 gases: the stability of C2nH2 (n=2–5) and C10

Carbon clusters and hydrocarbon molecules and radicals produced by laser vaporization of graphite in a hydrogen (H2 or D2) gas expansion source were studied using 10.5 eV one-photon ionization followed by time-of-flight mass spectroscopy. By changing the delay time of the ionization pulse relative to the vaporization pulse, we found two distinctly different mass patterns: rather non-selective signals of Cn (n=6–20) and CnHm (n=3–20 and m=1–4) at shorter delay times, while selective signals of C2nH2 (n=2–5) and C10 at longer delay times. The selective formation of the carbon cluster and hydrocarbon molecules at longer delay times is attributed to the relatively inert nature of polyynes H(–CC–)nH (n=2–5) and monocyclic C10. The formation mechanism of these hydrocarbons and carbon clusters by laser ablation under hydrogen gas is discussed.