Measurement of Low Energy Scattering Cross Sections for the He–N2 System

Total elastic scattering cross sections for the He–N2 system were measured for relative velocities from 1.68× 104 to 1× 105 cm/sec utilizing the crossed beam technique. An orbiting resonance below the j=0 to 2 transition was observed. Two collimated, aerodynamically intensified molecular beams intersecting at 10° were used. Each beam had a speed distribution comparable to that obtained from mechanical velocity selectors. The scattering center density was determined from a calibration of the detector utilizing a thermal beam source, carefully considering the geometry of the system. Attenuation of the scattering signal due to the background gas was determined without recourse to pressure-gauge readings. One beam was modulated and integrating techniques were used to recover the signal. The time-of-flight technique was used to determine the initial conditions in each beam. The measurements were compared with quantum mechanical calculations performed at the University of Bonn using a LJ (12,6) potential. Generally, the measurements were larger than these calculations, but one resonance was partially resolved.