Profile of the 9.85-GHz Neutral Hydrogen Line Taking into Account the Zeeman Effect (Computations and Solar Observations)

The 9.85-GHz (3.04 cm) line of atomic hydrogen due to the 2²P_3/2–2²S_1/2 transition between levels of the hyperfine structure occupies a special place in the complex spectrum of the Sun. This is essentially the only hydrogen line that is expected in the solar radio spectrum. The promising nature of solar observations in the H_3.04 line was first noted in 1952 by Wild, who calculated the line profile using a model for the "quiet" Sun characterized by a weak magnetic field (several Gauss). Computations of this line profile taking into account the strong magnetic fields in solar active regions (hundreds Gauss) are considered here. It is shown that the Zeeman effect leads to appreciable changes in the appearance of the line profile. This may help explain why searches for the H_3.04 line have not led to any detections earlier. New observations of the Sun on the RATAN-600 telescope are analyzed with allowance for the Zeeman effect.