where A1, A2, and B2 are the generalized Hanstorp coefficients describing the relative scaling of the p → d over p → s, d → f over d → p, and p → d over d → p photodetachment channels, respectively. In the limit of 𝛾 = 1 (e.g., for O2  ), eqn ( . The Hanstorp coefficients are not entirely independent of each other: treating the radial parts of the p and d components of the MO as hydrogenic functions, 𝐴 , 𝐴 , and 𝐵 can be expressed in terms of two effective charges, 𝜁 and 𝜁 , describing the p and d contributions to the MO. 𝐴 is defined by 𝜁 , 𝐴 by 𝜁 , while 𝐵 -by both 𝜁 and 𝜁 and can therefore be determined from the two A coefficients. Yet, this still leaves five parameters (𝛾 , 𝜁 , 𝜁 , 2,0, and 3,1 or, equivalently, 𝛾 , 𝐴 , 𝐴 , 2,0, and 3,1). While these properties can be, in principle, evaluated by ab initio methods, they are often used as empirical fitting parameters. Unfortunately, such black-box application of the model amounts to fitting experimental data with a many-parameter function: an adequate fit can usually be obtained, but the physical insight is limited.