An experimental setup has been implemented to obtain absolute total electron detachment cross sections and relative ionization cross sections in the energy range 50-7000 eV in gas-phase collisions between anionic beams and neutral molecular targets. The primary anionic beam (O2-) is produced through a pulsed hollow cathode discharge-induced plasma, deflected and focused towards the collision region where the molecular target is maintained at a well-known pressure. Electron detachment cross sections are measured from the attenuation of the O2- beam after interaction with N2 molecules confined in a gas cell. Negative and positive fragment ions produced during the collisions are extracted and mass analyzed by time-of-flight mass spectrometry. Relative ionization cross sections are derived from the ratio of the measured positive ion fragment intensities (N2+, N+) to the primary O2- beam intensity.