On the Zeeman effect of 2Π states in diatomic molecules

The theory of the Zeeman effect in ²Π states of diatomic molecules is reconsidered. Second order terms due to the interaction with ²Δ states, which were left out in a previous investigation, are now included. The total correlation between the spin-rotation coupling constant and the centrifugal distortion in the spin-orbit coupling renders the fitted molecular g factors somewhat ambiguous. This problem is handled by a transformation of the basis for the Hamiltonian matrix. The theoretical results are exemplified for the ²Π ground state of OH for which EPR data are available for both the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ substates. A combination of ab initio predictions and fitted values of the g factors finally yields new information concerning the separate contributions from ²Σ⁺, ²Σ^?, and ²Δ states to the contamination of the ²Π ground state in OH.