Measurement of OH radicals at state X ²Π in an atmospheric-pressure micro-flow dc plasma with liquid electrodes in He, Ar and N₂ by means of laser-induced fluorescence spectroscopy

The density of OH radicals in ground state is measured by laser-induced fluorescence (LIF) spectroscopy in the core of a micro-flow discharge in He, Ar and N-2 with a water electrode. The lines P-2(6), P-1(4) and P-2(3) of the X (2)Pi (v '' = 0) to the A(2)Sigma(+) (v' = 1) transition are used for OH radical excitation. The density of the main quencher of OH radical in the core of the discharge is estimated based on the time decay of the LIF signal. It is revealed that the plasma core consists of a high amount of 8-10% of water vapour. The calculation of the absolute density of OH radical is carried out based on the model of LIF excitation including vibrational and translation energy transfer, and the results in different gases are presented for the discharge