Effect of hydrogen bonding on the infrared absorption intensity of OH stretch vibrations

Abstract

We consider how the infrared intensity of an O-H stretch in a hydrogen bonded complex varies as the strength of the H-bond varies from weak to strong. We obtain trends for the fundamental and overtone transitions as a function of donor-acceptor distance R, which is a common measure of H-bond strength. Our calculations use a simple two-diabatic state model that permits symmetric and asymmetric bonds, i.e. where the proton affinity of the donor and acceptor are equal and unequal, respectively. The dipole moment function uses a Mecke form for the free OH dipole moment, associated with the diabatic states. The transition dipole moment is calculated using one-dimensional vibrational eigenstates associated with the H-atom transfer coordinate on the ground state adiabatic surface of our model. Over 20-fold intensity enhancements for the fundamental are found for strong H-bonds, where there are significant non-Condon effects. The isotope effect on the intensity yields a nonmonotonic H/D intensity ratio as a function of R, and is enhanced by the secondary geometric isotope effect. The first overtone intensity is found to vary non-monotonically with H-bond strength; strong enhancements are possible for strong H-bonds. Modifying the dipole moment through the Mecke parameters is found to have a stronger effect on the overtone than the fundamental. We compare our findings with those for specific molecular systems analysed through experiments and theory in earlier works. Our model results compare favourably for strong and medium strength symmetric H-bonds. However, for weak asymmetric bonds we find much smaller effects than in earlier work.

Puzzle of the Intramolecular Hydrogen Bond of Dibenzoylmethane Resolved by Molecular Dynamics Simulations

“…34,50 On the basis of quantum chemical calculations, Hansen et al proposed that the O−H stretching frequency is close to 1550 cm −1 and responsible for the strong band seen at that wavenumber. 52 This conclusion is in line with a significant enhancement of the intensity, ν OH , due to the electric anharmonicity for hydrogen bonds whose donor−acceptor distances are in the range of 2.4−2.5 Å, as predicted by Athokpama et al 53 Petkovićand Etinski examined the structure of an isolated DBM molecule and its ν OH frequency using quantum chemical methods and dimensionally reduced models of the potential energy surface. 54 The potential energy barrier for the proton transfer was computed to be in the range from 0.8 to 2.0 kcal/ mol depending on the employed electronic structure method and basis set.…”

Synthesis, spectroscopic (FT–IR and UV–Vis), crystallographic and theoretical studies, and a molecular docking simulation of an imatinib-like template

“…Pyridin-2-amine shows an experimental as N-H band at 3445 cm À1 (Bü yü kmurat et al, 1999; Mary et al, 2010). When comparing this value with the calculated value of the studied molecule, a red shift is observed (Athokpam et al, 2017), perhaps caused by the formation of dimers involving N-HÁ Á ÁN hydrogen bonds (Fig. 2).…”

Vibrational Ultra Strong Coupling of Water and Ice

“…Second, the large fosc values of the OH (OD) stretches of water and ice originate from intermolecular hydrogen bonding, which can enhance fosc by a factor of 26 and 38 when water vapor condenses to liquid water and ice, respectively. 33,[38][39][40] This situation is in sharp contrast with the general trend for the other molecular vibrations because in general, the ratio of fosc in the liquid phase to that in the gas phase is described as (n + 2) 2 /9n (n: refractive index of molecular liquid), 31,33 the value of which is no more than two because n < 2 for normal molecular liquids. The intermolecular hydrogen bonding also explains why the OH (OD) stretches of alcohols are second to those of ice and water in the size order of ΩR since the fosc enhancement is also found for OH (OD) stretches of alcohols.…”