Bandwidth Dependence of Measured uv Absorption Cross Sections of Argon*

Abstract

The atomic-absorption cross section of neutral argon between the P232 and P212 states of the Ar+ ion has been measured at an instrumental bandwidth of 0.04 Å. Accurate line shapes for the (3s)2 (3p)5 P212nd′ transitions have been obtained for n = 9 to 20. Also presented are oscillator strengths and line positions for transitions having n = 9 to 30. In the course of this investigation an analysis was made of the effect of instrumental bandwidth on measured absorption cross sections and line shapes in the ultraviolet. It is demonstrated that, contrary to the assumption made by many uv-spectroscopists, a linear Beer’s law plot does not necessarily indicate that a true peak or minimum absorption cross section has been measured. Errors of as much as a factor of two can be introduced by this assumption. The results presented in this paper have been corrected for this effect. Discrepancies between these and earlier measurements are shown to be consistent with the analysis.