Measurement of absolute differential cross sections for vibrational excitation of O-2 by electron impact

New measurements of absolute differential cross sections (DCSS) for vibrational excitation of O-2, With improved sensitivity and resolution, are presented. The 90 degrees DCSS are given as a function of energy up to 16 eV for elastic scattering and vibrational excitation of up to upsilon = 7. A weak continuous, probably non-resonant, background scattering is found in the upsilon = 1 cross section in addition to the well known sharp (2) Pi(g) resonances dominating vibrational excitation in the energy range up to 2.5 eV. The sharp (2) Pi(g) resonances interfere coherently with the background scattering both in the upsilon = 1 and in the elastic channels. New absolute values for the energy-integrated DCSS for (2) Pi(g) resonances are given. They exhibit oscillatory Franck-Condon factors in the upsilon = 4-7 exit channels. The broad resonance peaking at 9 eV, dominating vibrational DCSS at higher energies, causes excitation of high vibrational levels (up to the dissociation limit) of the X(3) Sigma(g)(-) ground state, but not of the a(1) Delta(g) and b(1) Sigma(g)(+) electronically excited states, supporting its assignment as the (4) Sigma(u)(-) resonance, the selectivity being caused by spin selection rules. The excitation of high v's indicates a relatively narrow autodetachment width for this resonance. The angular dependence at 9 eV is, however, not a simple p(sigma) wave as would be expected for a simple sigma(mu)* shape resonance. Preliminary experiments with a free jet cooled sample, concerned with rotational broadening of the (2) Pi(g) resonance, are reported.