An electrospray ionization flow tube study of the protonated betaine/ammonia complex

Reactions of protonated betaine, BetH(+), with ammonia and deuterated ammonia were studied under thermal conditions with a combination of an electrospray ionization (ESI) source and a flow tube reactor. Reaction with NH, in a flow tube pressure range of 0.1-0.45 Torr leads, with a low reaction efficiency of 0.034 +/- 0.011, to formation of a collisionally stabilized protonated betaine/ammonia complex, which can have the ion/dipole BetH(+).NH3, structure and/or the ammonium ion stabilized salt-bridge complex structure, Bet.NH4+. Reaction with ND, leads to a highly efficient H/D exchange of the labile hydrogen of BetH(+) presumably via the excited, chemically activated, salt-bridge complex, [Bet.ND3H+]*. Ions selected from the ESI source upstream in the flow tube, or generated by the reactions with ammonia midstream and then collisionally stabilized and thermalized to 292 +/- 3 K by collisions with He or Nz carrier gas species at 0.23 +/- 0.01 Torr were subjected to multi-collision-induced dissociation (CID) with He or N-2, just before sampling. ClD is achieved by raising the potential of the sampling nose cone from 0 to -20 V. The threshold voltage required for multi-collision-induced dissociation of the protonated betaine/ammonia complex to BetH+ and NH3, is considerably lower than the threshold voltage for dissociation of the protonated betaine homodimer, (Bet)(2)H+ in accord with the lower binding energy of the former. (C) 2000 Elsevier Science B.V.