Mechanism of Collisional Spin Relaxation in Triplet-Sigma Molecules

Abstract

We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold 3 Σ molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in collisions with 3He and 4He. The 4He data support the predicted 1=B2 e dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant Be. The measured 3He rate coefficients are much larger than the 4He coefficients, depend less strongly on Be, and theoretical analysis indicates they are strongly affected by a shape resonance. The results demonstrate the influence of molecular structure on collisional energy transfer at low temperatures.