C I as a radiometer of RELICT radiation in cosmological epochs of Z greater than or equal to 2

The possibility of using neutral carbon absorption as an indicator of the cosmic background radiation temperatures at early cosmological epochs is discussed. It is shown that the excitation temperature of low density interstellar neutral carbon may be equated with the relict radiation temperature, which would be strong enough to populate the fine-structure levels of C I only at epochs corresponding to redshifts greater than or equal to 2. Such fine-structure lines may then be observed and their equivalent widths analyzed to determine excitation temperatures in high-resolution absorption spectra of C I UV lines in quasars.