No abstract

Absolute differential, integral and momentum transfer cross sections for electronmethane collisions were determined using a crossed beam spectrometer for impact energies from 1.5-100 eV and angles from 10'-130". Comparison with published total woss sections shows good agreement. At the shape resonance (7.5 eV) excitation measurements of the two vibrational peaks were taken and the angular distribution or their DCS was determined.The elastic ucs are compared with recent meamrcments and theoretical calculations.

Differential scattering cross sections (DCS) for electron-CF4 collisions in the energy range from 1.5 to 100 eV were measured with a crossed beam instrument for scattering angles of 15' to 130'. The DCS are normalized by reference to He. Integral and momentum transfer cross sections are compared with measurements of total cross sections, swarm experiments and theory. The integrated DCS show a broad structure at 7 eV of symmetry T2 as predicted by theory, and one broad peak from 15 to 25 eV. The observed peaks differ in magnitude and angular distribution from recent SMC calculations. Evidence of a shape resonance of T2 symmetry was observed in the recorded angular distributions for vibrational modes nu 0, nu 1, nu 3, and nu 4. In addition a large cross section for nu 3 excitation with 2 eV electrons was found to occur by a direct mechanism.

Differential cross sections for electron impact vibrational excitation of ethane (C,H,) have been determined for incident energies from 3 to 20 eV over a scattering angular range of 20" to 130". In addition, vibrational excitation functions were determined for impact energies of 2 to 15 eV at scattering angles of 30", 60", 90" and 120". These measurements confirm the broad shape resonance at 7.5 eV but provide no evidence for a (second) resonance near 2.3 eV. A decomposition of the vibrational energy-loss spectrum shows strong resonance enhancement of selected vibrational modes, which may be explained by decay of a temporary negative ion ( T N I ) of symmetry species e,. A continuum multiple scattering calculation (CMS) reproduces these experimental results fairly well and indicates the simultaneous involvement of a T N I of species a*".

Cross sections for vibrationally elastic scattering of the system e-C2H6 have been measured with a newly constructed apparatus of the crossed-beam type using the relative flow technique. Absolute elastic differential cross sections for C2H6 were obtained by measuring the ratios to the cross section for He at impact energies of 2, 3, 4, 5, 6, 7.5, 8.5, 10, 15, 20, 40 and 100 eV and angles from 15' to 130'. Integral and momentum transfer cross sections were calculated from the DCS and are compared with other measurements. A short description of the apparatus is given.