Electron-impact fragmentation dynamics of carbonyl sulfide: A combined experimental and theoretical study

In this study, we examine the interaction of low- to intermediate-energy electrons $(0--45\phantom{\rule{0.28em}{0ex}}\mathrm{eV})$ with carbonyl sulfide. These collisions lead to the formation of several anionic fragments, including ${\mathrm{C}}^{\ensuremath{-}}, {\mathrm{O}}^{\ensuremath{-}}, {\mathrm{S}}^{\ensuremath{-}}$, and ${\mathrm{SO}}^{\ensuremath{-}}$. When the incident electron energy is below the first ionization potential of the molecule, the dissociative electron attachment (DEA) process dominates, primarily yielding ${\mathrm{O}}^{\ensuremath{-}}$ and ${\mathrm{S}}^{\ensuremath{-}}$ fragments. At higher energies, beyond the ionization potential, ion-pair dissociation becomes the dominant process, resulting in the emergence of additional fragments such as ${\mathrm{C}}^{\ensuremath{-}}$ and ${\mathrm{SO}}^{\ensuremath{-}}$. This leads to an increasingly intricate mechanism, necessitating a detailed analysis to elucidate the ion-pair dissociation pathways. The absolute cross section for ${\mathrm{S}}^{\ensuremath{-}}$ ions has been determined using the well-established relative flow technique. Theoretical cross sections are calculated using the multiconfigurational time-dependent Hartree method, with each potential energy curve obtained from equation-of-motion coupled-cluster singles and doubles calculations. The computed values are in excellent agreement with the experimental data. The analysis reveals that both linear and bent anionic resonant states contribute to the dissociation process. As the electron energy increases, nuclear rearrangement becomes an indispensable component of the fragmentation dynamics. Due to low count rate, only relative cross section curves have been obtained for the ${\mathrm{O}}^{\ensuremath{-}}$ and ${\mathrm{SO}}^{\ensuremath{-}}$ ions. At higher energies, the ion-pair thresholds are evaluated using the Wannier threshold law, yielding values consistent with those derived from thermochemical data.