The reactions of C(3P) with H2, HCl, HBr, and CH3OH(D) were investigated in a crossed-beam configuration using laser ablation of graphite as the source of C(3P). Upon pulsed irradation of graphite with focused laser output at 266 and 355 nm, hyperthermal C(3P) is produced and expands freely into the vacuum. In this "free ablation" mode, directional beams of monomeric carbon are produced with a peak velocity of ∼8000 m s-1 and a broad velocity distribution that can be described by temperatures of ∼21 000 and ∼9500 K when using 266 and 355 nm ablation wavelengths, respectively. Using 266 nm ablation, the endothermic reactions of C(3P) with the title molecules were investigated by probing the CH product. CH is produced predominantly in v = 0 with rotational distributions that are well described by temperatures in the range 1500-2200 K, depending on the molecular reactants. The spin-orbit and Λ-doublet sublevels are equally populated. In reactions with CH3OD, both CH and CD are detected, identifying both the methyl and the hydroxyl groups as reactive sites. Comparisons with the CH internal energy distributions obtained in the reaction of C(1D) with H2 show remarkable similarities. On the basis of theoretical investigations and the known electronic states of the methylene intermediate, it is suggested that the reactions of both C(3P) and C(1D) proceed via insertion involving carbene intermediates. The participation of several low-lying states of the carbenes may lead both to lowering of the activation barrier for insertion and to CH products with similar populations of the two Λ-doublet components.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry