Prospect for vibrational transition frequency measurement of rare-gas hydride ions

A method of precise measurement of the X¹Σ(v, J, F) = (0, 0, 1/2) - (1, 1, 1/2) transitions in HeH⁺ (89.1 THz), NeH⁺ (81.3 THz), and ArH⁺ (77.1 THz) molecular ions is proposed. These E1-allowed transitions are useful for locking the frequencies of infrared lasers because they are free from electric-quadrupole shifts. The DC Stark and Zeeman shifts are suppressed to below 10⁻¹⁶. The molecular ions are prepared in the (0, 0, 1/2) state using a cryogenic chamber without optical pumping. Measurements with low systematic uncertainty using a small number of molecular ions is possible by quantum logical spectroscopic detection of the (0, 2, 3/2) state to which molecular ions are pumped by the clock laser. (author)