Reinvestigation of spectroscopic properties for ammonia–hydrogen halide complexes from Car–Parrinello Molecular Dynamics

Infrared spectra of ammonia–hydrogen chloride and hydrogen bromide were obtained from Car–Parrinello Molecular Dynamics simulations. Proton distribution and proton transfer free energy along hydrogen bond together with hydrogen bond angle distribution during the simulations have been calculated. VPT2 and VSCF anharmonic vibrational frequencies have been also computed at DFT (BLYP) and post-Hartree–Fock (MP2) levels. Hydrogen bond properties obtained from MD simulations show good agreement with previously reported static results. In the absence of experimental gas phase infrared spectra, reported results shed further light on the spectroscopic properties of ammonia–hydrogen halides molecular complexes.