Two-dimensional penning ionization electron spectroscopy of HCl with He*(2³S) atom

Penning ionization of HCl upon collision with metastable He*(2³S) atoms was studied by two-dimensional (collision-energy/electron energy resolved) Penning ionization electron spectroscopy and by classical trajectory calculations. Collision energy resolved studies enable us to obtain important information about stereo dynamical aspects on this reaction; sideways approaches of the He* atoms on H-Cl molecular axis play a dominant role in the ionization event for producing HCl⁺(X ²Π_i, v′ = 0,1), and glancing collision is one of the dominant trajectories of the He* atoms to produce HCl⁺(A, ²Σ⁺). It was also found that the formation of vibrationally excited HCl⁺(X ²Π_i, v′ > 1) through the unidentified HCl** Rydberg state was influenced by a strong attractive interaction, whereas the formation of the HCl** Rydberg state, dissociating to H(1s) and autoionizing Cl**(¹D₂ nl) atoms, was found to be affected by a repulsive interaction around the Cl end of the HCl molecule.