H2 dissociation in Ar–H2 arc discharge of moderate pressure

Abstract

The line intensity ratio technique for estimation of hydrogen-to-argon density ratio and hydrogen molecule dissociation degree in arc discharge in Ar–H2 mixtures at moderate pressures (2–3 Torr) is analyzed. Intensity ratios of three hydrogen lines of Balmer series (Hα (656.3 nm), Hβ (486.3 nm) and Hγ (434.0 nm)) to ArI 750.4 nm (2p1 → 1 s2) and ArI 811.5 nm (2p9 → 1s5) lines were examined. Effect of Ar fraction in Ar–H2 mixtures on the diagnostic technique and molecular hydrogen dissociation degree in the large-volume high-density moderate-pressure Ar–H2 arc was studied. Using ArI 811 nm line for the intensity ratio diagnostics in the arc discharge is not valid due to great role of the excitation from 1s5 in production of Ar 2p9 level. It is shown that to obtain the correct H density value it is necessary to account quenching of H* excited states by Ar atoms and H2 molecules. Pair of Hα and ArI 750 nm lines is the best choice for determining atomic hydrogen density using HI-to-ArI line intensity ratio technique because of the upper excited state of Hα (n = 3) is less subjected to quenching by Ar atoms and H2 molecules as compared with higher H* levels (n = 4, 5). It is shown increasing Ar fraction in Ar–H2 mixtures results in growth of the molecular hydrogen dissociation degree.