The Zeeman Effect in the OH Bands

Abstract

Apparatus and experimental procedure. The Zeeman effect in the $^{2}\ensuremath{\Sigma}\ensuremath{\rightarrow}^{2}\ensuremath{\Pi}$ OH bands in the near ultraviolet has been photographed with a 21-foot grating at 7 field strengths, varying from 5000 gauss to 34000 gauss. Up to 22000 gauss a discharge in water vapor was used as the source. Two types of quartz tubes were employed, one viewed laterally, the other end-on and placed between rectangular pole-faces. At high fields the Back-box arc, operating in water vapor, was employed.Nature of the OH bands. The structure of the bands is briefly reviewed. New data on the satellite lines are presented, from which the $\ensuremath{\rho}$-type doubling in the $^{2}\ensuremath{\Sigma}$ states for which $v=0 \mathrm{and} 1$, is found to be 0.216 ($K+\frac{1}{2}$). Wave-number data on the hitherto unobserved $^{\mathrm{PP}}P_{21}$ branch are also given. The agreement between the calculated and observed wave numbers, as well as the Zeeman effect, establishes the identity of this branch.Theoretical calculation of the Zeeman patterns in OH. Hill's theory of the Zeeman effect in doublet states is applied to OH. In the $^{2}\mathrm{II}$ state the molecule behaves in the field as though quite rigid, symmetrical patterns being produced. The exact treatment of a $^{2}\ensuremath{\Sigma}$ molecular state, is given here for the first time. This state gives rise to large magnetic energy patterns which are shown in diagrams, as are also the resulting Zeeman spectrum patterns. The variety of ordering of the magnetic levels in the two states involved is the cause of strange patterns, consisting, for all lines except those near the origin, of a narrow concentrated part and a wide diffuse part.Results and comparison with the theory. The results of observations on the Zeeman patterns are given in tables and diagrams and quantitatively compared with the theoretical expectations. The lines are treated in three groups, (1) lines near the origin, whose fine structure is resolved, (2) lines of intermediate ${J}^{\ensuremath{'}\ensuremath{'}}$ whose patterns were completely observed, (3) lines of larger ${J}^{\ensuremath{'}\ensuremath{'}}$. The agreement with the theory is satisfactory.