REACTIONS OF HYPERTHERMAL C(P-3) GENERATED BY LASER-ABLATION WITH H-2, HCL, HBR, AND CH3OH

The reactions of C(P-3) with H-2, HCl, HBr, and CH3OH(D) were investig ated in a crossed-beam configuration using laser ablation of graphite as the source of C(P-3). Upon pulsed irradation of graphite with focus ed laser output at 266 and 355 nm, hyperthermal C(P-3) is produced and expands freely into the vacuum. In this ''free ablation'' mode, direc tional beams of monomeric carbon are produced with a peak velocity of similar to 8000 m s(-1) and a broad velocity distribution that can be described by temperatures of similar to 21 000 and similar to 9500 K w hen using 266 and 355 nm ablation wavelengths, respectively. Using 266 nm ablation, the endothermic reactions of C(P-3) with the title molec ules were investigated by probing the CH product. CH is produced predo minantly in upsilon = 0 with rotational distributions that are well de scribed by temperatures in the range 1500-2200 K, depending on the mol ecular reactants. The spin-orbit and Lambda-doublet sublevels are equa lly populated. In reactions with CH3OD, both CH and CD are detected, i dentifying both the methyl and the hydroxyl groups as reactive sites. Comparisons with the CH internal energy distributions obtained in the reaction of C(D-1) with H-2 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(P -3) and C(D-1) 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 pr oducts with similar populations of the two Lambda-doublet components.