Sensitivity of microwave spectra of deuterated ammonia to variation of electron-to-proton mass ratio

We estimate sensitivity coefficients Q_\mu to variation of the electron-to-proton mass ratio \mu for microwave transitions in partly deuterated ammonia NH2D and ND2H. Because of the mixing between rotational and inversion degrees of freedom the coefficients Q_\mu strongly depend on the quantum numbers of the transition. This can be used for astrophysical search for possible variation of the constant \mu.
Comment: 7 pages, submitted to J. Phys. B, Special Issue on High Precision Atomic Physics; v2: corrected misprints in Tab. 2&3