Lifetime measurement of the first vibrationally excited state of MgH+ in a cryogenic Paul Trap (CryPTEx)

A method is presented to measure the decay rate of the first excited vibrational state of polar molecular ions being part of a Coulomb crystal in a cryogenic linear Paul trap. Specifically, we have monitored the decay of the |v=1,J=1>_X towards the |v=0,J=0>_X level in MgH⁺ by saturated laser excitation of the |v=0,J=2>_X - |v=1,J=1>_X transition followed by state selective resonance-enhanced two-photon dissociation out of the |v=0,J=2>_X level. The technique can be extended to other simple molecular ions and it enables the determination, with an accuracy at the few percent level, of decay rates and thus absorption strengths.