Ab initio Calculation of the Dipole Moment Function of the OH Radical Ground State

Recently it has been theoretically predicted and experimentally confirmed that at altitudes of 80-110 km from the Earth's surface the signals of the global navigation satellite systems (GNSS) are delayed as a result of a multiple resonance scattering by the Rydberg complexes. The attenuation of GNSS signals occurs mainly in the lower atmosphere layers, where the greatest effect is achieved through interaction with charged aerosol layers. A thunderstorm conditions are of particular interest whereby the presence of strong electric fields and hydration of aerosols can lead to the detachment of OH radicals from water clusters. Since the spectrum of radiation and absorption of these radicals for rotational transitions is part of the microwave range, they are expected to make an additional resonance contribution to the delay of radio signals thus necessitating a detailed study of the electronic structure of the OH radical. This paper offers the ab initio calculations of the dipole moment function for the ground X-2 state of the OH molecule using the dipole length approach and the finite-field method. The comparison with the experiment shows that in extended model spaces the approximation of the dipole length leads to more accurate values of the dipole moment than the finite-field method.