title: Mechanism of collisional spin relaxation in 3sigma molecules.
abstract: We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold 3Sigma 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/B_{e};{2} dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant B_{e}. The measured 3He rate coefficients are much larger than the 4He 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.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Wesley C
authors.initials: WC
authors.lastname: Campbell
authors.forename: Timur V
authors.initials: TV
authors.lastname: Tscherbul
authors.forename: Hsin-I
authors.initials: HI
authors.lastname: Lu
authors.forename: Edem
authors.initials: E
authors.lastname: Tsikata
authors.forename: Roman V
authors.initials: RV
authors.lastname: Krems
authors.forename: John M
authors.initials: JM
authors.lastname: Doyle