Physical properties of DC discharge generated in He, Ar, N$_{2}$ and Air bubbles in liquid

DC excited discharge in liquid generated in bubbles of different gases (He, Ar, Air, N$_{2})$ has been investigated. V/C characteristics and emission spectra have been recorded in the range of discharge current from 10 up to 30 mA. Visual view of the discharge by fast imaging technique shows that plasma consists of filaments propagated in bubble in case of N$_{2}$ and Air and uniformly distributed in bubble in He and Ar. Gas temperature has been determined by simulation of OH band with different T$_{rot}, $T$_{vib}$. Fitting of the experimental spectra has been carried out with two different rotational temperatures in order to take into account overpopulation of the OH radicals V/T distribution. It was revealed that for 5 micosS/cm conductivity T$_{rot}$ in He discharge is 1200 K at I=10 mA and linearly increase up to 1600 K with grows of the current. Similar increase of T$_{rot}$ from 1100 K (10 mA) to 1700 K (30 mA) is observed in Ar bubble discharge. In N$_{2}$ and Air plasma gas temperature is higher and almost constant at different currents: N$_{2}$ discharge T$_{rot}$=2200 K (10 mA) and 2500 K (30 mA); Air discharge T$_{rot}$=2200 K (current 10-30 mA).