Collision-energy-resolved Penning ionization electron spectroscopy of OCS with He*(23S) metastable atoms

Collision-energy dependence of partial Penning ionization cross-sections (CEDPICS) of OCS was obtained from collision-energy/electron-energy-resolved two-dimensional spectrum with a highly sensitive electron energy analyzer. The negative CEDPICS for X2Π and C2Σ+ states indicates attractive interaction around S and O atoms with He*(23S), where the corresponding 3π(S3p–O2p) and 8σ(σCO) orbitals extend, respectively. Utilizing classical trajectory calculations for CEDPICS and optimization of model potential energy surface, a large ring-like attractive well with a depth of ca. 120 meV was found for perpendicular directions around CS axis and smaller interaction was found in the collinear direction of the CO axis with well depth of ca. 70 meV around the oxygen atom in the lone pair region by sp2 hybridization.