Ion Spectroscopy of Vibrational and Vibronic Excitation in He+-O2Collisions

Abstract

Ion energy-loss spectra were measured for He + -O 2 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 X 3 Σ g - and vibronic excitation to the first excited state a 1 Δ g of O 2 are clearly resolved. The relative differential cross sections of vibronic excitation to a 1 Δ 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.