Ion Spectroscopy of Vibrational and Vibronic Excitation in He⁺–O₂ Collisions

抄録

Ion energy-loss spectra were measured for He⁺–O₂ collisions at the laboratory impact energy of 50 eV and scattering angles of 1≤θ≤8° by the use of a novel ion source which can produce a nearly monochromatic beam with high intensity. Peaks corresponding to vibrational excitation of the electronically ground state X³Σ_g⁻ and vibronic excitation to the first excited state a¹Δ_g of O₂ are clearly resolved. The relative differential cross sections of vibronic excitation to a¹Δ_g at the collision energy of 50 eV show humps at the scattering angles of θ>4°. This implies that a drastic change in the mechanism of the electronic excitation to the a state takes place around the scattering angle of 4°, and it induces highly vibrational excitation of the a state at larger scattering angles.