A "modified Lennard-Jones oscillator" model for diatom potential functions

A flexible new analytical representation for the internuclear potential ene rgy of a diatomic molecule is proposed and tested. The new model may be tho ught of as a generalization of the prototypical Lennard-Jones (2n,n) functi on, with the form V(R)=D-e[1-(R-e/R)(n)e(-beta(z)z)](2), where z=(R- R-e)/( R+R-e) is a dimensionless radial distance variable which approaches 1 as R -->infinity. This form explicitly incorporates the theoretically predicted attractive inverse-power asymptotic behavior V(R)=D-C-n/R-n associated with most potential energy curves. This "modified Lennard-Jones" (MLJ) function is tested against other flexible forms for the potential energy by perform ing nonlinear least-squares fits both to known numerical potential curves a nd to spectroscopic line positions. (C) 2000 American Institute of Physics. [S0021-9606(00)00909-0].