Mechanism of Collisional Spin Relaxation in \(^3\)Σ 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 \(^3\)He and \(^4\)He. The \(^4\)He data support the predicted 1/B\(^{2}_{e}\) dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant B\(_e\). The measured \(^3\)He rate coefficients are much larger than the \(^4\)He coefficients, depend less strongly on B\(_e\), 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.