Electron-impact dissociative excitation of [Formula Presented] [Formula Presented]: Detection of light fragment ions [Formula Presented] and [Formula Presented]

Absolute cross sections are reported for the electron-impact dissociative excitation of the deuterated hydrocarbon ions [Formula Presented] [Formula Presented] from threshold to 70 eV using a crossed beams technique. The method focuses on detecting and measuring light dissociation-product ions from a heavy target. The ion targets are typical of those formed in the discharge ion source, and some may be in excited electronic and/or vibrational states. A common feature of the studied targets was a dominant [Formula Presented] formation cross section with almost the same absolute value of [Formula Presented] [Formula Presented] for all [Formula Presented] from 25 to 70 eV. The present measurements are compared with the available data, and for [Formula Presented] from [Formula Presented] and [Formula Presented] the data agree well with recent results obtained with the storage-ring technique.