Survey of Negative-Ion—Molecule Reactions in O2, CO2, H2O, CO, and Mixtures of These Gases at High Pressures

Abstract

The negative-ion species produced in O2 and some gases containing oxygen have been surveyed for various pressure and E/p conditions using an rf mass spectrometer coupled to an electron drift tube operating at pressures up to 5 torr. The gases studied include O2, CO2, H2O, and CO as well as the mixtures CO2–O2, H2O–O2, CO–O2 at moderate and high E/p. When CO2 is present, O2− and O− are converted to CO4− and CO3−, respectively. The rate coefficients for these reactions at 300°K are approximately 1.3×10−29 and 8×10−29 cm6/sec, respectively. When H2O is present, complex ions such as (H2O)n·O2−, (H2O)n·O− and (H2O)n·OH− are formed with n≤5. In CO–O2 and H2–O2 mixtures, ion destruction, consistent with associative detachment of O−, has been observed to proceed with rate coefficients of about 10−9 cm3 sec−1.