Spin depolarization ofN2+(Σ2+)in collisions withH3eandH4ein a magnetic field

Abstract

We study the effect of a magnetic field on the spin-depolarization cross sections of $\text{N}_{2}{}^{+}(^{2}\ensuremath{\Sigma})$ in collisions with $^{3}\text{H}\text{e}$ and $^{4}\text{H}\text{e}$ at very low collision energy. The fundamental states of the two nuclear spin isomers of $\text{N}_{2}{}^{+}$ are shown to respond quite differently to the application of the field. When the applied magnetic filed increases, the spin-depolarization cross sections are found to monotonously decrease for the fundamental paralevel $N=0$ of $\text{N}_{2}{}^{+}$ whereas they monotonously increase for the fundamental ortholevel $N=1$ of $\text{N}_{2}{}^{+}$. This effect is found to be amplified around the resonances and an explanation based on the different mechanism of spin flipping acting for these two levels is proposed. We discuss the sensitivity of the results on the change of relative mass when $^{3}\text{H}\text{e}$ is replaced by $^{4}\text{H}\text{e}$. We also explore the tuning of the inelastic cross sections by examining the variation of the scattering length as a function of the magnetic field and locate several narrow Feshbach resonances.