Vibrational spectrum of the formic acid dimer in the OH stretch region. A model 3D study

The vibrational spectrum of the formic acid dimer in the OH stretch region is calculated by solving a 3D vibrational Schrödinger equation and employing an electronic potential and dipole moment calculated at the MP2 level of theory. Two Raman-active bands of the symmetric OH stretch fundamental are located around 2600 cm−1; the gap between them (∼300 cm−1) is caused by concerted proton tunneling. IR-active bands around 3100 cm−1 are assigned to the antisymmetric OH stretch fundamental, its first overtone and two complex transitions. The calculated H/D isotope effect on the intensity of the antisymmetric OH fundamental is 1.92.