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We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6-12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned them as proceeding via shape resonances with temporary occupation of s * O-H orbitals. These low energy fragmentations become much stronger in the larger molecules and the strongest DEA process in the compounds with two hydroxyl groups, which thus represent an intermediate case between the behavior of small alcohols and the sugar ribose which was discovered to have strong DEA fragmentations near zero electron energy [S. Ptasin´ska, S. Denifl, P. Scheier and T. D. Ma¨rk, J. Chem. Phys., 2004, 120, 8505]. Above 6 eV, in the Feshbach resonance regime, the dominant process is a fast loss of a hydrogen atom from the hydroxyl group. In some cases the resulting (M À 1) À anion (loss of hydrogen atom) is sufficiently energyrich to further dissociate by loss of stable, closed shell molecules like H 2 or ethene. The fast primary process is state-and site selective in several cases, the negative ion states with a hole in the n O orbital losing the OH hydrogen, those with a hole in the s C-H orbitals the alkyl hydrogen.

New measurements of absolute differential cross sections (DCSS) for vibrational excitation of O2, 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 v=7. A weak continuous, probably non-resonant, background scattering is found in the v=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 v=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 v=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 a1 Delta g and b1 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 vs indicates a relatively narrow autodetachment width for this resonance. The angular dependence at 9 eV is, however, not a simple psigma wave as would be expected for a simple sigma u* shape resonance. Preliminary experiments with a free jet cooled sample, concerned with rotational broadening of the 2 Pi g resonance, are reported.

Absolute differential cross sections for excitation of helium by electron impact are reinvestigated within the first 4 eV above threshold at scattering angles of 20, 60, 90 and 120' with improved resolution and statistical accuracy. Cross sections are reported for the n=2, n=3, 43S and 53S states. The new results permit a more accurate assessment of the widths and shapes of the threshold features, in particular for the 23S and the 21S states, which are in very good agreement with the published results of R-matrix calculations. Structures caused by doubly excited Wannier ridge resonances are observed in all cross sections. Their intensities in the individual decay channels are informative of the energy partition of the excited electron pair and their shapes exhibit interesting regularities.