Delayed fragmentation of ethylene and allene induced by electron impact

Abstract

We experimentally investigated the delayed fragmentation processes of ethylene and allene dications induced by 300-eV electrons with the cold target recoil ion momentum spectroscopy in an observation window up to \ensuremath{\sim}2 \ensuremath{\mu}s. For each molecule, several distinct pathways involving prompt or delayed fragmentations were observed and relative branching ratios among them were analyzed. According to the time-of-flight coincidence measurements of corresponding recoil ionic fragments, the survival times and thus lifetimes from nanoseconds to microseconds of different delayed-dissociative precursor dications were retrieved. Besides the two-body channels, i.e., ${\mathrm{H}}^{+}+{\mathrm{C}}_{2}{{\mathrm{H}}_{3}}^{+}$ and ${\mathrm{H}}^{+}+{\mathrm{C}}_{3}{{\mathrm{H}}_{3}}^{+}$, the delayed deprotonation was also observed in many-body channels, i.e., $\mathrm{H}+{\mathrm{H}}^{+}+{\mathrm{C}}_{n}{{\mathrm{H}}_{2}}^{+}$ ($n=2$, 3) and $2\mathrm{H}/{\mathrm{H}}_{2}+{\mathrm{H}}^{+}+{\mathrm{C}}_{3}{\mathrm{H}}^{+}$. The lifetimes of the metastable intermediate diacations ${\mathrm{C}}_{n}{{\mathrm{H}}_{3}}^{2+}$ and ${\mathrm{C}}_{3}{{\mathrm{H}}_{2}}^{2+}$ were estimated.