Local thermodynamic equilibrium of an arc over an ice surface

A study of the emission spectra from discharges on an ice surface and a discussion of its implication on local thermodynamic equilibrium are presented. Rotational temperatures were measured using OH (A-X) emission bands. The variation of rotational temperature, which is similar to that of gas temperature with discharge current, was studied. The excitation temperature of the arc column was determined using the ratio of spectral line intensities as well as the Boltzmann method. Electron densities were estimated by analyzing the Balmer line H_α profile, broadened by the Stark effect. Differences between the rotational and excitation temperatures showed that the arc formed over an ice surface is not in a state of thermal equilibrium.