ABSTRACT
The exchange reaction is believed to be the result of collisions between sample ions (HR~, H^RD^) and reagent gas neutrals R'OD. At 0.5 to 1.0 torr pressure, each ion suffers up to several hundred collisions with neutrals (pri marily the reagent gas) before exiting the ion source. On the other hand, the probability of multiple collisions of a given sample molecule with reagent ions is very low because of the low concentrations of each; this rules out significant exchange by a reaction sequence such as
H^R + R'OD^ -> H .R D ^ + R 'O D ( 1)
H.RD^R'OD HRD H-R'ODH^ (2)
HRD -r R'OD! HRD.^ + R'OD (3)
Rather, the incorporation of deuterium into the sample ion must occur during the lifetime of the ion/molecule collision complex formed when the sample ion and the deuterium-labelled reagent gas collide.
