DIRECT EVIDENCE FOR PREFERENTIAL BETA-C-H BOND-CLEAVAGE RESULTING FROM 248 NM PHOTOLYSIS OF THE N-PROPYL RADICAL USING SELECTIVELY-DEUTERATED 1-BROMOPROPANE PRECURSORS

A series of selectively-deuterated 1-bromopropane precursors have been used to study site-specific photolysis in the n-propyl radical. A two -color photolysis approach (222 nm followed by 248 nm radiation) is us ed to create an intermediate photofragment and produce an H or a D ato m, which is detected by 1 + 1 resonance ionization through Lyman-alpha . Target precursors are BrCH2CD2CD3, BrCD2CH2CD3, and BrCD2CD2CH3 as w ell as BrCD2CH2CH3, BrCH2CD2CH3, and BrCH2CH2CD3. The ''enhanced'' H ( or D) atom signals clearly demonstrate that C-H (or C-D) bond cleavage at the beta position is strongly favored. The net enhancement process undoubtedly involves photolysis of an intermediate, almost certainly the n-propyl radical. A comparison with systems involving ethyl and is opropyl radical photolysis is also presented.