Sensitivity coefficients to temporal variation of the fine-structure constant $\alpha$ for transitions between the fine-structure (FS) sublevels of the ground states of C I, Si I, S I, Ti I, Fe I, N II, Fe II, O III, S III, Ar III, Fe III, Mg V, Ca V, Na VI, Fe VI, Mg VII, Si VII, Ca VII, Fe VII, and Si IX are calculated. These transitions lie in the mid- and far-infrared regions and can be observed in spectra of high-redshift quasars and infrared bright galaxies with active galactic nuclei. Using FS transitions to study $\alpha$ variation over cosmological time scales allows one to improve the limit on $\Delta \alpha /\alpha$ by several times as compared to contemporaneous optical observations $\left(\left|\Delta \alpha /\alpha \right|<{10}^{-5}\right)$, and to suppress considerably systematic errors of the radial velocity measurements caused by the Doppler noise. Moreover, the far infrared lines can be observed at redshifts $z\gtrsim 10$, far beyond the range accessible to optical observations $\left(z\lesssim 4\right)$. We have derived a simple analytical expression which relates the FS intervals and the sensitivity of the FS transitions to the change of $\alpha$.

• Received 3 February 2008

DOI:https://doi.org/10.1103/PhysRevA.77.032119