Dissociative ion-pair formation in collisions of fast potassium atoms with benzene and fluorobenzene

Using a crossed molecular-beam technique, electron transfer is studied in collisions of fast potassium atoms with benzene and fluorobenzene molecules. The negative fragment ions formed in the collision region are extracted by a pulsed voltage, and their masses and energy release distributions analyzed by a time-of-flight (TOF) method. The dominant fragment from C₆H₅F is F^¯. The phenyl ring fragments CH^¯ and C₂H^¯ are also observed but with lower intensities. In the case of C₆H₆ the dominant anionic specie is C₂H^¯. The kinetic-energy release distributions of the various fragments are derived from the width and shapes of the TOF peaks in the spectrum.