An ion storage exchange collision experiment on heavy paramagnetic ions is proposed to study the possibility of using a hyperfine structure transition of Hg⁺ as the basis of a new primary frequency standard. All known limitations of the accuracy, with the exception of the second order Doppler effect and of the rms frequency stability, are expected to be smaller than 10^-14. Methods are discussed to reduce the second order Doppler effect and to increase the rms frequency stability by cooling the ions and by stabilizing their temperature.