Knowledge Bank

Varitation of the $C12-C13$ ratio in carbonates of the aragonite lattice leads to fine structure in the 12$\mu$ region whose spacing and qualitative intensity can be fitted satisfactorily by the introduction of a nearest neighbor coupling constant in the potential energy. The coupling constant is believed to arise from dipole-dipole forces. From the coupling constant the value of the CO bond moment is found to be $1.52\pm 0.1$ debyes in $BaCO3$, $1.56\pm 0.1$ debyes in $SrCO3$. The coupling is so large in $CaCO3$ (on account of the inverse cube dependence upon interdipole distance) that the perturbation theory cannot be applied without modification.