A proposal is given to use the transition of the HeH+ (2.0 THz), NeH+ (1.0 THz), and ArH+ (0.62 THz) molecular ions as novel frequency standards in the terahertz region. This transition is free from the electric-quadrupole shift, and the DC Stark and Zeeman shifts are much less than those of the CaH+ and MgH+ molecular ions. These transitions are useful for locking the frequencies of oscillators like quantum cascade lasers (QCL) or resonant tunnel diodes (RTD) with uncertainties of 10−15.

Molecular rotational transition frequencies are useful as frequency standard in the terahertz region. The transition frequencies of QH+ molecular ions (Q: an even isotope of Group II element) in a linear trap are useful as measurement uncertainties are low. An uncertainty given by the Stark and Zeeman shifts can be below 10−15 using 202HgH+ molecular ion.

No abstract