ABSOLUTE INELASTIC DIFFERENTIAL ELECTRON-SCATTERING CROSS-SECTIONS FOR HE, XE, N-2 AND CO AT NEAR-THRESHOLD IMPACT ENERGIES FOR 90-DEGREES SCATTERING ANGLE

An electron time-of-flight (TOF) technique was utilized to obtain abso lute differential cross sections for electron impact excitation in He, Xe, N-2 and CO at near-threshold impact energies at 90 degrees scatte ring angle. These cross sections are more reliable that those obtained from conventional beam-beam scattering measurements using electrostat ic spectrometers and can serve as secondary standards for normalizing relative scattering intensities. The results obtained from the TOF mea surements are significant also because they fill the gap between cross sections available at very near threshold and intermediate impact ene rgies.