Thermal decomposition of H3O- produced in reaction of OH- with H2CO

Viggiano, A. A.; Miller, Thomas M.; Miller, Amy E. Stevens; Morris, Robert A.; Paulson, John F.; Brown, Eileen R.; Sutton, Emmett A.
January 1994
Journal of Chemical Physics;1/1/1994, Vol. 100 Issue 1, p357
Academic Journal
The ion–molecule reaction OH-+H2CO→H3O-+CO has been studied at 300 K with isotopic labeling of reactants. The H3O- product is only observed in small abundance because the ion dissociates into OH-+H2 upon multiple collisions in a helium buffer gas. Without isotopic labeling, the pseudo-first-order kinetics plots for the reactions of OH- with H2CO and OD-+D2CO were found to be curved as a result of the regeneration of OH- or OD- reactant. A scavenger technique was used to remove the H3O- (or D3O-) produced prior to dissociation, to reveal the true first-order attenuation of OH- (or OD-) in reaction with H2CO (or D2CO). The rate constant for the OH-+H2CO reaction is 7.6×10-10 cm3 s-1, and for OD-+D2CO is 5.7×10-10 cm3 s-1. For the isotopically mixed cases OH-+D2CO and OD-+H2CO, the rate constants are equal to 1.3×10-9 cm3 s-1, about twice as large as those for the reactions involving only a single hydrogen isotope, indicating that isotopic exchange is an important process. The rate constants for the thermal dissociation of H3O- and D3O- in helium were found to be 1.6×10-12 and 1.1×10-12 cm3 s-1, respectively, within a factor of 2. The results are discussed in terms of other thermal dissociation reactions of ions.


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