Low-frequency electromagnetic radiation of hydrogen molecular gas: effect of the ortho-para conversion

We calculate the rate of the spontaneous magnetic dipole radiation transitions from ortho- to para-states of the hydrogen molecule at the room temperature with the radiation wavelengths about 0.01 - 0.1 cm. Exponentially small differences between the rotational energies and heat capacities of parahydrogen and orthohydrogen molecules and also diatomic molecules consisting of different hydrogen atoms for high temperatures are derived.