On the use of total cross sections for obtaining the anisotropic interaction potential in atom–diatom system

A study is made of the ’’conservation of the total cross section’’ and the ’’equivalence of the total cross section’’ rules for scattering from H2. It is shown that these rules are a better approximation than the random phase approximation would indicate. Cross section formulas are given for scattering atoms from mj state selected molecules and it is shown that total cross sections for state selected molecules depend on the anisotropic part of the interaction potential, while the spin-averaged total cross section often depends only on the spherically symmetric part of the interaction potential. The total spin-averaged cross section is thus independent of the initial rotation state of the molecule and depends only on the relative collision energy. It is further demonstrated that isotopic substitution, which shifts the center of mass changing the symmetric part of the interaction potential, has too small an effect on the total cross section to be useful as a means of determining the anisotropy of the potential.