Some effects in the spectra of individual sparks between copper electrodes electroplated with thin deposits of silver were studied with the aid of a time-resolving spectrograph. The initial phase of the discharge is characterized by short-lived broadened lines of N II and O II, plus an intense continuum. The line spectrum is predominantly that of Ag II with but a few lines of Ag I present. All of the high-level lines of Ag II, and only these lines, are initially asymmetrically broadened and shifted to the red, but return to their normal wavelength positions after 6–9 µsec; while the low-level lines are characterized by self-reversal and associated continuum. The strong similarity to the spectrum of exploding Ag wire indicates that the same mechanism is operative in both. These effects are explained in terms of a Stark effect induced by the fields of neighboring electrons and ions.
LEON BLITZER, "Shifts and Asymmetries in Condensed Spark Spectra of Electroplated Electrodes," J. Opt. Soc. Am. 45, 564-567 (1955)