The total scattering cross sections for H2+H2, D2+D2, and HD+HD for relative collision energies below 10 meV

Relative total scattering cross sections for normal H2+normal H2, para-H2+para-H2, normal D2+normal D2, ortho-D2+ortho-D2, and HD+HD were measured at energy below 10 meV by colliding particles from two inclined nozzle beams. Cross sections for the H2+H2 pairs were measured over a relative velocity range of 200–1450 m/s; the normal H2+normal H2 results suggest a l=3 orbiting resonance near 375 m/s while the para-H2+para-H2 results have a l=4 orbiting resonance near 585 m/s. This latter resonance has a peak energy of 1.79 meV and a FWHM of 1.05 meV. The D2+D2 cross sections were measured over the velocity range of 190 to 1000 m/s and a minimum between the l=4 and l=5 orbiting resonances was observed. Some preliminary measurements on HD+HD over the range of 250–1250 m/s indicate a possible l=4 orbiting resonance near 300 m/s. The experimental work compares favorably to cross sections calculated from a theoretical potential.