Understand
Microwave and submillimeter molecular transition frequencies between nearly degenerated rotational levels, tunneling transitions, and mixed tunneling-rotational transitions show an extremely high sensitivity to the values of the fine-structure constant, alpha, and the electron-to-proton mass ratio, mu.
- This review summarizes the theoretical background on quantum-mechanical calculations of the sensitivity coefficients of such transitions to tiny changes in alpha and mu for a number of molecules which are usually observed in Galactic and extragalactic sources, and discusses the possibility of testing the space- and time-invariance of fundamental constants through comparison between precise laboratory measurements of the molecular rest frequencies and their astronomical counterparts.
- In particular, diatomic radicals CH, OH, NH+, and a linear polyatomic radical C3H in Pi electronic ground state, polyatomic molecules NH3, ND3, NH2D, NHD2, H2O2, H3O+, CH3OH, and CH3NH2 in their tunneling and tunneling-rotational modes are considered.
- It is shown that sensitivity coefficients strongly depend on the quantum numbers of the corresponding transitions.