Infrared spectral-shift induced by hydrogen bonding cooperativity in cyclic and prismatic water clusters

Abstract

A direct representation of the cooperative vibrating properties of hydrogen bonds (H-bonds) is presented for cyclic and prismatic water clusters. Through collaborating nuclear vibrations, which are inherent in H-bonding, these weak bonds constitute a simple form of cooperativity, which gives H-bonds an unexpectedly amplified effect. Hence, abnormal shifting activities of infrared vibration modes are observed. The nuclear vibrating patterns clearly reveal that H-bonds retain three effects: i) arousing collective nuclear vibrations, ii) intensifying donor symmetric stretching modes (Symst), and iii) inhibiting donor asymmetric stretching modes (Asyst). H-bonds in aqueous systems show diverse cooperative behavior that originates from the versatile assembly of water molecules. For the first time, we directly show that “coherent” H-bonds reinforce Symst and restrict Asyst extremely powerfully, in contrast to incoherent H-bonds. However, anharmonic nuclear vibrations partially destabilize the cooperative effects of H-bonds. Beyond the present model systems, our findings advance a new perspective on the intrinsic cooperativity of H-bonding, and should stimulate incentives for future spectroscopic and biological dynamic studies.