The effect of large amplitude motions on the transition frequency redshift in hydrogen bonded complexes: A physical picture

Abstract

We describe the vibrational transitions of the donor unit in water dimer with an approach that is based on a three-dimensional local mode model. We perform a perturbative treatment of the intermolecular vibrational modes to improve the transition wavenumber of the hydrogen bonded OH-stretching transition. The model accurately predicts the transition wavenumbers of the vibrations in water dimer compared to experimental values and provides a physical picture that explains the redshift of the hydrogen bonded OH-oscillator. We find that it is unnecessary to include all six intermolecular modes in the vibrational model and that their effect can, to a good approximation, be computed using a potential energy surface calculated at a lower level electronic structure method than that used for the unperturbed model.

The effect of large amplitude motions on the vibrational intensities in hydrogen bonded complexes

“…26,27,36 Recently, we developed a vibrational model to describe the vibrational transitions in hydrogen bonded complexes, where the effect of the intermolecular modes is included as a perturbation on a LM model. 28 This Local Mode Perturbation Theory (LMPT) model was shown to calculate accurately the transition wavenumbers of the donor unit vibrations in water dimer. In the present article, we have extended the LMPT model to calculate oscillator strengths in addition to the transition wavenumbers.…”

“…If these modes are ignored in the vibrational model, it leads to large discrepancies between experimental and calculated vibrational frequencies. [26][27][28] Intensity studies of hydrogen bonded complexes are limited. Kjaergaard et al 29 compared the performance of the second order Vibrational Perturbation Theory (VPT2) method 30 with a three-dimensional harmonically coupled anharmonic oscillator (HCAO) local mode (LM) model 31 on the H 2 O· · ·H 2 O complex.…”

Communication: A rotationally resolved (2OH) overtone band in the water dimer (H2O)2

“…This is the usual case with van der Waals and hydrogen-bonded aggregates since the sophisticated detection and production means that are required to access high-resolution data on such weakly bound species are more typically available in these lower energy ranges. The NIR, overtone range received limited theoretical 9,15,20 and experimental 7 attention. In the latter work, Nesbitt and co-workers used vibrationally mediated dissociation data to investigate a supersonic expansion with water and Ar as carrier gas in the 2OH excitation range (1.4 μm).…”

Overtone spectroscopy of molecular complexes containing small polyatomic molecules

“…Refs. [267][268][269]), calling for and hopefully stimulating more investigations in the near future. In the simulation, optimal Lorentzian components of the linewidths were adjusted.…”