Force Constants of Diatomic Molecules. I. A General Semitheoretical Approach

A general method for calculating the quadratic, cubic, and quartic force constants of homonuclear diatomic molecules and binary hydrides is proposed. The scheme has been designed to be sufficiently simple for application to any molecule and represents an attempt to bridge the gap between atomic and molecular data. It uses as starting parameters only the orbital exponents and one‐electron, one‐center, kinetic‐energy integrals for the united and separated atoms. A distorting operator is defined and used to generate functions of the molecular orbital type. A scaling property of wavefunctions along the three independent Cartesian axes is invoked to calculate a reasonably close approximation to the kinetic energy of the electrons and its derivatives with respect to the internuclear coordinate. The virial method is used to calculate the force constant from these quantities. The method is applied to the elements of the first and second periods.