Nuclear Spin State Equilibration through Nonmagnetic Collisions

Abstract

For nonlinear molecules with equivalent identical nuclei an important pathway leading to equilibration of nuclear spin statistics isomers is provided by wavefunction mixing induced by the spin—rotation interaction and in some cases the spin—spin interaction. For CH4 this mixing is very large and provides for very rapid equilibration of the three spin statistics isomers. For asymmetric rotor molecules such as H2O and CH2O the rapidity of the equilibration is sensitive to the exact rotational energy level pattern. The spin—rotation mixing may be very important if there is an accidental near degeneracy of the right sort. Then most of the isomerization ``funnels'' through the near-degenerate levels.