Λ -doublet spectra of diatomic radicals and their dependence on fundamental constants

Λ-doublet spectra of light diatomic radicals have high sensitivity to the possible variations in the fine-structure constant α and electron-to-proton mass ratio β. For molecules OH and CH sensitivity is further enhanced because of the J-dependent decoupling of the electron spin from the molecular axis, where J is total angular momentum of the molecule. When Λ-splitting has different signs in two limiting coupling cases a and b, decoupling of the spin leads to the change in sign of the splitting and to the growth of the dimensionless sensitivity coefficients. For example, sensitivity coefficients for the Λ-doublet lines J=9/2 of the Π1/2 state of OH molecule are on the order of 10³.