Two-dimensional vibrational spectroscopy. IV. Relationship between through-space vibrational coupling and intermolecular distance

By means of the ab initio calculation, the second-order nonlinear derivatives of the dipole moment and polarizability of a dimer, CO⋯HCl, with respect to the two, CO and HCl, stretching modes are found to be inversely proportional to r³, where r is the intermolecular distance. The observed r-dependencies are interpreted by taking into account the dipole-induced-dipole interaction. Thus, it is shown that the intermolecular distance between two vibrational chromophores can be estimated by quantitatively examining the cross-peak intensity in a given 2D (two dimensional) vibrational spectrum.