Mechanism of Collisional Spin Relaxation in Triplet-Sigma Molecules

TL;DR

This study combines experimental measurements and theoretical analysis to understand how molecular structure influences Zeeman relaxation rates in cold triplet-sigma molecules colliding with helium, revealing the role of rotational splitting and shape resonances.

Contribution

It provides the first combined experimental and theoretical investigation of collisional spin relaxation in triplet-sigma molecules, highlighting the impact of rotational constants and shape resonances.

Findings

4He data support inverse square dependence on rotational constant B

3He rate coefficients are larger and less dependent on B due to shape resonances

Results show molecular structure significantly affects low-temperature collisional energy transfer

Abstract

We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold Triplet-Sigma 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 inverse square dependence of the collision induced Zeeman relaxation rate coefficient on the molecular rotational constant B. The measured 3He rate coefficients are much larger than 4He and depend less strongly on B, and the 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.