The role of electron correlation on calculated XH-stretching vibrational band intensities

XH-stretching vibrational band intensities have been calculated for seven small molecules with OH, NH and CH bonds, respectively, using the simple harmonically coupled anharmonic oscillator local mode model and ab initio dipole moment functions, both expressed in XH-stretching bond coordinates. The dipole moment functions were calculated with a triple valence basis set including both diffuse and multiple polarization functions, and at different levels of ab initio theory. The self-consistent field Hartree-Fock calculation is compared with different ways of including electron correlation. These calculations show that in general electron correlation in the ab initio calculation of the dipole moment function is often important in predictions of fundamental XH-stretching band intensities, whereas the XH-stretching overtone intensities are insensitive to electron correlation. This insight is important for studies of larger molecules where the highest levels of theory are not computationally feasible.