Laboratory Production of the Vegard – Kaplan Bands

Abstract

THE Vegard – Kaplan A ³∑ − X ¹∑ bands of nitrogen (N₂), some members of which are thought to occur in the spectrum of the upper air, usually require rather special conditions for production in the laboratory¹. Wulf and Melvin² and Janin³ have, however, shown that they are emitted readily from discharges through pure nitrogen in conventional ozonizers. As such tubes are somewhat inconvenient to set up and outgas, we have sought to modify them and have found the simple form shown diagrammatically in Fig. 1 quite effective. The left-hand section is a piece of ‘Pyrex’ tube, connected to a pumping train and sodium azide nitrogen generator through a trap cooled in liquid oxygen. The central section consists of the same tube flattened to a roughly circular disk 7 cm. in diameter, with its plane normal to the paper, and an internal clearance of 2–6 mm. The right-hand section is a ‘Pyrex’-quartz graded seal with a flat quartz end. A Tesla discharge is passed through the central section between disk electrodes (A,A′) pressed against its outer faces, and the spectrum observed through the quartz window. The discharge is a shower of small sparks, as described by Wulf and Melvin.