Photoionization produced by low-current discharges in O2, air, N2 and CO2

An analysis of gas ionization by the radiation produced in a low-current gas discharge is performed here on the basis of the comparison of measurements and the results of direct simulation of the excitation of identified extreme ultraviolet transitions, radiation transport and ionizing absorption of radiation. In unitary gases and in their mixtures with low admixtures of other gases, the ionizing radiation is generated in one electron impact by direct dissociative excitation and by direct ionizing excitation followed by a radiative transition of an excited neutral atom or ion, respectively. In N-2-O-2 mixtures, photoionization predominantly occurs via ionization of O-2 molecules due to the absorption of the emission produced by excited N-2 and, possibly, some N I, both produced by direct electron impact. The results obtained in this work provide the missing data required for performing direct numerical simulation of pre-breakdown phenomena, including the inception and propagation of coronas and creeping sparks, in the above-mentioned gases and mixtures.