Magnetic Trapping and Zeeman Relaxation of NH Molecules

NH molecular radicals are magnetically trapped in the presence of a helium buffer gas and their Zeeman relaxation and energy transport collisional cross-sections with helium are measured. Molecules are loaded from a molecular beam into a cold buffer gas cell in a 4T anti-Helmholtz magnetic trap. The NH-He energy transport cross-section is measured to be 2.7$\pm$ 0.8 $\times$10$^{-14}$cm$^{2}$ at 710 mK. The inelastic (Zeeman state changing) cross-section is also measured to be 3.8 $\pm$ 1.1$\times$10$^{-19}$cm$^{2}$ at 710 mK, indicating a $\gamma$ (elastic to inelastic cross-section ratio) of 7$\times$10$^{4}$, in agreement with the theory of Krems et al (PRA 68 051401(R) (2003)). Cross-section measurements are obtained for the interaction of the molecular isotopes $^{14}$NH, $^{14}$ND, $^{15}$NH and $^ {15}$ND with the helium isotopes He-3 and He-4.