Low-frequency radio recombination lines investigations

Radio spectroscopy at extremely low frequencies provides the unique opportunities for studies of the cold tenuous interstellar plasma. One of the most effective means for this - radio recombination lines of carbon - have been studied in many Galactic directions up to the decameter waves. In this review we report the main results of radio recombination lines investigations in the Institute of Radio Astronomy of National Academy of Sciences of Ukraine including development of corresponding tools and methods.