Mid- and far-infrared fine-structure-line sensitivities to hypothetical variability of the fine-structure constant

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 (vertical bar Delta alpha/alpha vertical bar<10(-5)), 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 greater than or similar to 10, far beyond the range accessible to optical observations (z less than or similar to 4). We have derived a simple analytical expression which relates the FS intervals and the sensitivity of the FS transitions to the change of alpha.