KINETIC-STUDIES OF NEGATIVE-ION REACTIONS IN A QUADRUPOLE ION-TRAP - ABSOLUTE RATE COEFFICIENTS AND ION ENERGIES

A new apparatus consisting of an ion-molecule reactor coupled to a qua drupole ion trap is described. The kinetics and products of the rapid reactions of SF6- with SO2, HNO3, and HCl in the ion trap are reported . There is excellent agreement between the ion trap rate coefficients and yields, and flowing afterglow results. Rate coefficients for react ions of products of the SF6- reactions are also reported. Measurements of the equilibrium constant for the reaction NO3-. HNO3+HNO3 reversib le arrow NO3-.(HNO3)(2) in the ion trap provide a very sensitive measu re of the energy of the trapped ions. These measurements indicate that the effective temperature of the trapped NO3-.(HNO3)(2) ion is 320 +/ - 30 K for an ion trap at 298 K (1-2 mTorr He, q(z) = 0.074). The pres ence of 0.2 mTorr N-2 buffer gas increases the internal temperature of the trapped ions by about 10 K. The internal temperature is also a we ak function of the trapping potential, increasing by about 10 K over t he range 0.074 < q(z) < 0.286.