Collisional Properties of Cold Spin-Polarized Nitrogen Gas: Theory, Experiment, and Prospects as a Sympathetic Coolant for Trapped Atoms and Molecules

Abstract

We report a combined experimental and theoretical study of collision-induced dipolar relaxation in a cold spin-polarized gas of atomic nitrogen (N). We use buffer gas cooling to create trapped samples of (^{14})N and (^{15})N atoms with densities (5(\pm)2) × (10^{12}) (cm^{-3}) and measure their magnetic relaxation rates at milli-Kelvin temperatures. These measurements, together with rigorous quantum scattering calculations based on accurate (ab) (initio) interaction potentials for the (^{7}\Sigma^{+}{u}) electronic state of (N{2}) demonstrate that dipolar relaxation in N+N collisions occurs at a slow rate of ~(10^{-13}) (cm^{3})/s over a wide range of temperatures (1 mK to 1 K) and magnetic fields (10 mT to 2 T). The calculated dipolar relaxation rates are insensitive to small variations of the interaction potential and to the magnitude of the spin-exchange interaction, enabling the accurate calibration of the measured N atom density. We find consistency between the calculated and experimentally determined rates. Our results suggest that N atoms are promising candidates for future experiments on sympathetic cooling of molecules.