Abstract
This paper describes a new technique for the experimental study of ions with organic radicals. A preliminary report has been published in J. Chem. Phys. 2004, 120, 3531, and we wish to communicate a complete description of this experiment. Clean, intense flows of hydrocarbon radicals/diradicals can be produced by a heated supersonic nozzle and are delivered to a flowing afterglow selected ion flow tube (FA-SIFT) instrument. The reactions of a simple radical, allyl (CH2CHCH2), and a diradical, ortho-benzyne (o-C6H4), with hydronium (H3O+) and hydroxide (HO-) ions were studied at thermal energy. We have studied the following reactions: CH2CHCH2 + H3O+ → C3H6+ + H2O, CH2CHCH2 + HO- → no product ions, o-C6H4 + H3O+ → C6H5+ + H2O, and o-C6H4 + HO- → C6H3- + H2O. We find that proton transfer reactions with H3O+ occur rapidly (the bimolecular rate constant, kII, is roughly 10-9 cm3 s-1). However, an unexpected result was obtained for o-C6H4 + HO-; the exothermic proton abstraction is significantly slower than the collision rate by nearly an order of magnitude (kII is approximately 10-10 cm3 s-1). We rationalize this by postulating a competing associative detachment. No charged products have been observed for CH2CHCH2 + HO-, presumably because of similar detachment pathways.
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