Search for the variation of fundamental constants: Strong enhancements in X Π 2 cations of dihalogens and hydrogen halides

We investigate a number of diatomic molecular ions to search for strongly enhanced effects of variation of fundamental constants important for physics beyond the standard model. The relative enhancements due to fine structure and electron-to-proton mass ratio variation occur in transitions between nearly degenerate levels of different nature. Since the trapping techniques for molecular ions have already been developed, the proposed molecules HBr+, HI+, Br2+, I2+, IBr+, ICl+, and IF+ are very promising candidates for future high-resolution experiments.