UV continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

The emission of the radiative dissociation continuum of the hydrogen molecule (a3Σ+g->b3&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 kinetics, rate constants of various collisional and radiative transitions, and fitting procedures made it possible to develop two methods of diagnostics of (1) the ground X1Σ+g state vibrational temperature Tvib from the relative intensity distribution, and (2) the rate of electron impact dissociation (d[H2]/dt)diss from the absolute intensity of the continuum. The known method of determination of Tvib from relative intensities of Fulcher-α bands was corrected and simplified due to the revision of d->a transition probabilities and cross sections of d2+Ar microwave discharges. In pure H2 plasma the values of Tvib obtained by two independent methods are in rather good accordance (Tvib= 3000-5000 K). In the H2+Ar microwave plasma it was observed that the shape of the continuum depends on the ratio of the mixture components. Absorption measurements of the population of the 3s23p54s levels of Ar together with certain computer simulations showed that the Ar*-> H2 excitation transfer plays a significant role. In our typical conditions (power flux: 4 W cm-2, pressure p = 0.5 mbar, H2:Ar= 1:1) the following values were obtained for the microwave discharge: (d[H2]/dt)diss approximately equals 2.5-5 × 1017 cm-3s-1. The contribution of the excitation transfer is about 10-30% of the total population of the a3Σ+g state.