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

Abstract

We report the observation of the hitherto undetected v = 8 ← 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 = 8 ← 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.

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

“…We reduce the motional temperature of the HD + ions by storing them together with Be + ions which are Doppler-cooled by a continuous wave (cw) 313 nm laser beam (see [18,23,24] for details). The rf trap is placed inside an ultrahigh vacuum chamber with a background pressure of 1 × 10 −10 mbar.…”

“…6). The apparatus and procedures for loading and compensation of stray electric fields are described in more detail in [18].…”

“…Following the approach of Koelemeij [18], we first ignore hyperfine structure and obtain transition dipole moments given by where χ v,L denotes the radial wavefunction of nuclear motion obtained by numerical solution of the radial Schrödinger equation, R stands for the internuclear separation, and D 1 (R) denotes the permanent electric dipole moment function of the 1sσ electronic ground state.…”

“…(7) and the fractional loss ǫ defined above. In previous work, it was assumed that S and ǫ are interchangeable [10,18,26,28]. In Appendix 2, we study the dependence of the signal S on the initial number of ions N i and the dissociated fraction ǫ in detail using realistic molecular dynamics (MD) simulations.…”

Bounds on fifth forces from precision measurements on molecules

“…Experiments on the v = 0 → 8 band in HD + are in preparation, with great potential for probing fifth force interactions, but no precision frequency results have been obtained yet [52].…”