Magnetic Rotation Spectra of the A 2Σ+ − X 2Πi Transition of OH and OD

The magnetic rotation spectrum of the (0, 0) band of the $A^2{\Sigma }^{+}{\mathrm{\hspace{0.17em}-\hspace{0.17em}X}}^2{\Pi }_i$ transition of OH (3064 Å) and OD (3065 Å) was photographed at high resolution along with the Zeeman and zero‐field absorption spectra. All twelve branches of both bands appeared with measurable intensities for the two magnetic fields used, 1300 and 2700 G. In each band the $P_1$ and $Q_1$ branches were the most intense, requiring only minutes of exposure compared to the four hours necessary for some weak branches. Several of the MRS lines (particularly in the OD spectra) revealed multiple structure where the individual Zeeman components appear unresolved in absorption. Interpretation was achieved by a computer‐aided synthesis of the spectra. Calculations were based on the classical formulas for the dispersion of the refractive index and absorption coefficient near resonance, and thus included the effects of both magnetic optical rotation and circular dichroism. After corrections for instrumental broadening, the calculations gave good agreement with experiment.