Very low energy electron scattering from benzene and deuterated benzenes

Measurements are reported of the absolute total cross sections for scattering of electrons between and 2 eV by and . Data are also recorded for scattering in the presence of an axial magnetic field over an energy range which extends from between 5 and 10 meV to 2.5 eV. Absolute values of the total scattering cross sections agree well with those of other groups down to 500 meV below which no other data are available. No differences in scattering cross sections are found within experimental error between and its deuterated derivatives. The shape resonance around 1.1 eV in is found at an energy above that for . This shift in energy is ascribed to the different zero-point energies of and , with a contribution from Jahn-Teller distortion in the temporary negative ion. Data at low electron collision energies show that the scattering cross section rises rapidly below 100 meV to values of 170- at the lowest energies. A combination of data obtained in the absence and presence of the axial magnetic field leads to the conclusion that attaches electrons at very low energy, in agreement with earlier high-pressure attachment studies. The lifetime of the moiety, however, appears to be of the order of microseconds - very much greater than had previously been suggested.