  The dilute ionized gas is very popular in the Universe. Usually only the
Compton interactions, the "Sunyaev-Zel'dovich" effect, were considered while
photons propagated in this medium. In this paper the "soft-photon process" is
considered. Due to the soft photons emitted during the propagation of a photon
in the dilute ionized gas, the main photon (propagating in the original
direction) will be redshifted. The formula to calculate this redshift is
derived.
