RELATIVISTIC PERTURBATION-THEORY OF MOLECULAR-STRUCTURE

The recently developed relativistic double perturbation theory is extended to handle relativistic changes of molecular structure more easily. This is achieved by simple coordinate scalings. Accurate higher order mixed perturbation energies for H-2+ are calculated. The relativistic changes of bond energy, DELTADE, of bond length, DELTAR(e), and especially of force constant, DELTAk, and of anharmonicity, DELTAa, are large, up to 100% . (Z/c)2. The dominant contributions to DELTAk and DELTAa are due to the "indirect" change of the nonrelativistic k and a connected with the relativistic change of bond length. Accordingly the relativistic changes obey Badger's and Gordy's rules (-DELTAR approximately DELTADE approximately DELTAk).