Continuous emission due to radiative ion-atom association and charge exchange in weakly ionized plasmas of H, He, Li and Na

The contribution of radiative charge exchange and radiative association in symmetrical ion-atom collisions to continuous EM radiation from weakly ionized gaseous plasmas has been considered within the semiclassical adiabatic theory. The differential (in lambda ) cross sections for spontaneous photon emission and the general expressions for the spectral coefficients of emission and absorption are given. The hydrogen and helium plasmas that are representative of two different optical types of gaseous medium have been studied in a broad range of T and lambda , 4000<or=T (K)<or=20000 and 200<or= lambda (nm) <or=1000. The domain of T and lambda , where ion-atom collisions contribute significantly to continuous plasma spectra, has been established. The case of weakly ionized alkali metal plasmas of Li and Na has been studied in the same interval of lambda but at lower temperatures, 1500<or=T (K)<or=3500. The relevance of the results to studies of laboratory plasmas is discussed.