Spin depolarization of N2+ (2Σ+) in collisions with 3He in a magnetic field: general behaviour and zero energy Feshbach resonances

Abstract

We give a brief account of the effect of a magnetic field on the spin-depolarization cross sections of N2+(2Σ) in collisions with 3He at very low collision energy. The fundamental states of the two nuclear spin isomers of N2+ are shown to respond quite differently to the application of the field. When the applied magnetic field increases, the spin depolarization cross sections are found to monotonously decrease for the fundamental para level N=0 of N2+, whereas they monotonously increase for the fundamental ortho level N=1 of N2+. 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 also explore the tuning of zero energy Feshbach resonances by examining the variation of the scattering length as a function of the magnetic field. We use the Smith Q matrix to calculate the lifetimes of the complexes associated with these resonances and discuss the law of variation as a function of the magnetic field of the Q matrix eigenvalues across such resonances.