Enhanced sensitivity to the fine-structure constant variation in Th IV atomic clock transition

Our calculations have shown that the 5f_5/2-7s_1/2 23131 cm^{-1} transition from the ground state in the ion Th^{3+} is very sensitive to the temporal variation of the fine structure constant alpha (q=-75300 cm^{-1}). The line is very narrow, the ion has been trapped and laser cooled and the positive shifter line 5f_5/2-5f_7/2 4325 cm^{-1} (q=+2900 cm^{-1}) may be used as a reference. A comparison may also be made with a positive shifter in another atom or ion. This makes Th^{3+} a good candidate to search for the alpha variation.