The low-lying 2Σ− states of OH

Potential energy curves for the two lowest 2Σ− states of OH are computed at the configuration-interaction level using four different basis sets. Electronic transition dipole moments connecting the excited 1 2Σ− and 2(D)2Σ− states with each other and with the ground X 2Π state are presented as functions of internuclear distance. The theoretical absorption oscillator strengths for the D 2Σ−(v′=0) ← X 2Π(v″=0) transition are in good agreement with the empirical value derived from astronomical measurements. The photodissociation cross sections for absorption from the v″=0, 1, and 2 levels of the ground state into the continuum of the 1 2Σ− state are calculated, and the interstellar and cometary photodissociation rates are derived.