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 C6 H5 F is F-. The phenyl ring fragments CH- and C2 H- are also observed but with lower intensities. In the case of C6 H6 the dominant anionic specie is C2 H-. The kinetic-energy release distributions of the various fragments are derived from the width and shapes of the TOF peaks in the spectrum.