Cold collisions of PH (3Σ-) with helium in magnetic fields

A theoretical investigation of the He-PH (3Σ-) complex is presented. We perform ab initio calculations of the interaction potential energy surface and discuss its error bounds with relevance to cold collisions, and we carry out accurate calculations of bound energy levels of the complex including the molecular fine structure and magnetic-field effect. We find the potential has two shallow minima and supports ten and 13 bound levels in complex with 3He and 4He, respectively. Based on the potential the quantum scattering calculations are then implemented for elastic and inelastic cross sections of the magnetically trappable low-field-seeking state of PH (3Σ-) in collision with 3He atom. The cold-collision properties and the influence of the external magnetic field as well as the effect of the uncertainty of interaction potential on the collisionally induced Zeeman relaxation are explored and discussed in detail. The ratio of elastic to inelastic cross sections is large over a wide range of collision energy, magnetic field, and scaling factor of the potential, so that helium buffer-gas loading and evaporative cooling of PH is a good prospect.