STUDIES OF NEGATIVE-ION-MOLECULE REACTIONS IN ENERGY REGION FROM O TO 3 EV

A modulated retarding-potential-difference technique has been used to define the energy width of an electron beam located in the source region of a time-of-flight mass spectrometer. Negative ions with energies in the region 0-3 eV are produced by dissociative electron attachment to gas molecules in this source and are permitted to react for a controlled continuously variable length of time with neutral molecules to produce secondary negative-ion products. From the observed time development of the reactions, the reaction rate constant may be obtained, and the cross section then calculated if the primary-ion velocity is known. Results are presented for the reactions O- + NO2 → NO2- + O, H- + H2O → OH- + H2, and D- + D2O → OD- + D2 at a number of primary ion energies, and for the reactions O- + N2O → NO- + NO, HCOO- + SF6 → SF5-* + (HCOOF), and SF6- + HCl → F2Cl- + (SF4H) at single energy points. © 1969 The American Physical Society.