Carbon atoms molecular beam studies

Molecular Beam Studies of Carbon Atom Reactions. 493... 

MOLECULAR BEAM STUDIES OE CARBON ATOM REACTIONS... 

In molecular beam studies of C atom reactions, it is also possible to select higher energy portions of the beam that contain C( D). This selection has been accomplished in a study of the reaction of singlet carbon with acetylene that proceeds with loss of hydrogen to give 116 (Eq. 66)." In contrast, C( P) reacts with acetylene by two channels producing both 116 and 117 (Eq. 67)." ... 

Since molecular beam investigations of C atom reactivity differ from other C atom studies with regard to dissipation of reaction exothermicity, it is difficult to compare them with other methods. A hallmark of carbon molecular beam studies is the fact that addition of C is followed by loss of H. This reaction path is unimportant in other reactions of C atoms. 

The surface chemical composition of InP as a function of thermal cleaning temperature was studied by Cheng, et al. (19), also using AES. They used an arsenic molecular beam and temperature of about 500 C to clean a freshly oxide passivated InP. The surface oxides are replaced by arsenic oxides which then vaporize at these temperatures. An atomically flat and carbon contamination free surface was obtained, as monitored in situ with AES and RHEED OJ). 

B. Cross Section Measurements In recent years crossed molecular beam techniques have been employed by Lee and co-workers ( ) to study extensively Ihe reactions of fluorine atoms with several different olefins. Very high cross-sections were observed, consistent with the rapid thermal rate constants measured above. In these ejqieriments, multichannel decomposition is observed (i. e., loss of H or CH3 after F addition to the ff -bond). Since the C-F bond is stronger dian any other single bond with a carbon atom, C-F bond scission teck to the original reactants does not compete with the exothermic processes involving breakage of C-C and C-H bonds. A tabulation of AH values for addition reactions of thermal F to various olefins is included (Table II) ( ). Some hi ly endothermic pathways are listed for the purposes of comparison. The ei eri-mental measurements of D/S in this table confirm that the only radicals undergoing appreciable C-C bond rupture with carbene formation after thermal F addition are those that form CF2. The extraordinary stability of the CF2 radical makes C-C bond rupture exothermic for these radicals. 

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