Observation of the v′=8←v=0 vibrational overtone in cold trapped HD+

We report the observation of the hitherto undetected v'=8a dagger v=0 vibrational overtone in trapped HD+ molecular ions, sympathetically cooled by laser-cooled Be+ ions. The overtone is excited using 782 nm laser radiation, after which HD+ ions in v=8 are photodissociated by the 313 nm laser used for Be+ cooling. The concomitant loss of HD+ is detected by the method of secular excitation (Roth et al. in Phys. Rev. A. 74:040501(R), 2006). We furthermore present details of the experimental setup, and we show that results from spectroscopy of v'=8a dagger v=0 overtones in combination with accurate ab initio calculations may yield a new value for the proton-electron mass ratio with an accuracy of order 1 ppb.