Theoretical study of infrared spectra perturbed by uniform electric fields: A b i n i t i o calculations on H2O, NH3, H2CO, and C2H4

The changes in harmonic vibrational frequencies and line intensities with respect to different strengths of an applied electric field are computed using analytically calculated energy derivatives. The ground states of several small molecules are studied at the ab initio restricted Hartree–Fock self-consistent-field (RHF SCF) level with a double ζ plus polarization basis set. The dependence of vibrational frequencies and line intensities upon the applied field strength is discussed.