DEUTERIUM-EXCHANGE IN THE SYSTEMS OF H2O+ H2O AND H3O+/H2O/

The reactions of H2O+, H3O+, D2O+, and D3O+ with neutral H2O and D2O w ere studied by tandem mass spectrometry. The H2O+ and D2O+ ion reactio ns exhibited multiple channels, including charge transfer, proton tran sfer (or hydrogen atom abstraction), and isotopic exchange. The H3O+ a nd D3O+ ion reactions exhibited only isotope exchange. The variation i n the abundances of all ions involved in the reactions was measured ov er a neutral pressure range from 0 to 2 x 10(-5) Ton. A reaction schem e was chosen, which consisted of a sequence of charge transfer, proton transfer, and isotopic exchange reactions, Exact solutions to two gro ups of simultaneous differential equations were determined; one group started with the reaction of ionized water, and the other group starte d with the reactions of protonated water. A nonlinear least-squares re gression technique was used to determine the rate coefficients of the individual reactions in the schemes from the ion abundance data. Branc hing ratios and relative rate coefficients were also determined in thi s manner. A delta chi-squared analysis of the results of the model fit ted to the experimental data indicated that the kinetic information ab out the primary isotopic exchange processes is statistically the most significant, The errors in the derived values of the kinetic informati on of subsequent channels increased rapidly, Data from previously publ ished selected ion flow tube (SIFT) study were analyzed in the same ma nner, Rigorous statistical analysis showed that the statistical isotop e scrambling model was unable to explain either the SIFT or the tandem mass spectrometry data. This study shows that statistical analysis ca n be utilized to assess the validity of possible models in explaining experimentally observed kinetic behaviors. Published by Elsevier Scien ce B,V.