uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

The emission of the radiative dissociation continuum of the hydrogen molecu le (a(3)Sigma(g)(+) --> b(3)Sigma(u)(+) electronic transition) is proposed to be used as a source of information for the spectroscopic diagnostics of nonequilibrium plasmas. The detailed analysis of excitation-deactivation ki netics, rate constants of various collisional and radiative transitions, an d fitting procedures made it possible to develop two methods of diagnostics of (1) the ground X(1)Sigma(g)(+) state vibrational temperature T-vib from the relative intensity distribution, and (2) the rate of electron impact d issociation (d[H-2]/dt)(diss) from the absolute intensity of the continuum. The known method of determination of T-vib from relative intensities of Fu lcher-alpha bands was corrected and simplified due to the revision of d --> a transition probabilities and cross sections of d <-- X electron impact e xcitation. General considerations are illustrated with examples of experime nts in pure hydrogen capillary-are and H-2 + Ar microwave discharges. In pu re H-2 plasma the values of T-vib obtained by two independent methods are i n rather good accordance (T-vib = 3000-5000 K). In the H-2 + Ar microwave p lasma it was observed that the shape of the continuum depends on the ratio of the mixture components. Absorption measurements of the population of the 3s(2)3p(5)4s levels of Ar together with certain computer simulations showe d that the Ar* --> H-2 excitation transfer plays a significant role. In our typical conditions (power flux: it 4 W cm(-2) pressure p = 0.5 mbar, H-2:A r = 1:1) the following values were obtained for the microwave discharge: (d [H-2]/dt)(diss) approximate to 2.5-5 x 10(17) cm(-3) s(-1). The contributio n of the excitation transfer is about 10-30 % of the total population elect ronic of the a(3)Sigma(g)(+) state. [S1063-651X(99)04903-X].