Decay rate measurement of the first vibrationally excited state of MgH$^+$ in a cryogenic Paul trap
Abstract
We present a method to measure the decay rate of the first excited vibrational state of simple polar molecular ions being part of a Coulomb crystal in a cryogenic linear Paul trap. Specifically, we have monitored the decay of the $|ν$=$1,J$=$1 \rangle_X$ towards the $|ν$=$0,J$=$0 \rangle_X$ level in MgH$^+$ by saturated laser excitation of the $|ν$=$0,J$=$2 \rangle_X$-$|ν$=$1,J$=$1 \rangle_X$ transition followed by state selective resonance enhanced two-photon dissociation out of the $|ν$=$0,J$=$2 \rangle_X$ level. The technique enables the determination of decay rates, and thus absorption strengths, with an accuracy at the few percent level.