Optimizing the resolution of the alternating-gradient m/μ selector

We study the focusing of large neutral molecules in a molecular beam using electric fields. Since all quantum states of these molecules are high-field seeking under the practical experimental conditions, alternating gradient (AG) focusing has to be applied. The optimal ac frequency that yields the highest transmission depends on m/μ, where μ is the dipole moment and m denotes the mass. Therefore, an AG focuser can be used to select species with different m/μ ratios, e.g., the conformers of neutral molecules [Phys. Rev. Lett. 100, 133003 (2008)]. Here we demonstrate both theoretically and experimentally how the resolution of such an m/μ selector can be optimized.