Dynamics of weak, bifurcated, and strong hydrogen bonds in lithium nitrate trihydrate

The properties of three distinct types of hydrogen bonds, namely a weak, a bifurcated, and a strong one, all present in the LiNO₃·(HDO) (D₂O)₂ hydrate lattice unit cell are studied using steady-state and time-resolved spectroscopy. The lifetimes of the OH stretching vibrations for the three individual bonds are 2.2 ps (weak), 1.7 ps (bifurcated), and 1.2 ps (strong). For the first time, the properties of bifurcated H bonds can thus be unambiguously directly compared to those of weak and strong H bonds in the same system. The values of their OH stretching vibration lifetime, anharmonicity, red shift, and bond strength lie between those for the strong and weak H bonds. The experimentally observed inhomogeneous broadening of their spectral signature can be partly attributed to the coupling with a low frequency intermolecular wagging vibration.