It long has been known that advantages attend employing, as a basic internuclear coordinate for determining a molecular potential energy surface, a variable S = 1 - R-0/R, where R-0 is a reference distance near to half of an equilibrium distance. For a diatomic molecule, starting from numerical or analytical representations of the energy, W(R) = W(S), it is shown how to generate the analytical series, W(S) = sigma(S)Sigma(n)b(n)P(n)(S), where P-n(S) are orthogonal polynomials with weight function sigma(S) over the range (-1, 1) for S. By rearrangement, there result the series for W(R) in inverse powers of R. For neutral diatomics, the Jacobi polynomials, p(n)(1.6) (S) with weight function (1 + S)(1 -S)(6), seem particularly appropriate when the potential for large R is of special interest.