Spectroscopic snapshots of the proton-transfer mechanism in water

Abstract

The Grotthuss mechanism explains the anomalously high proton mobility in water as a sequence of proton transfers along a hydrogen-bonded (H-bonded) network. However, the vibrational spectroscopic signatures of this process are masked by the diffuse nature of the key bands in bulk water. Here we report how the much simpler vibrational spectra of cold, composition-selected heavy water clusters, D(DO), can be exploited to capture clear markers that encode the collective reaction coordinate along the proton-transfer event. By complexing the solvated hydronium "Eigen" cluster [DO(DO)] with increasingly strong H-bond acceptor molecules (D, N, CO, and DO), we are able to track the frequency of every O-D stretch vibration in the complex as the transferring hydron is incrementally pulled from the central hydronium to a neighboring water molecule.

Identification of Active Sites and Structural Characterization of Reactive Ionic Intermediates by Cryogenic Ion Trap Vibrational Spectroscopy

“…The influence of the nature of the tagging species has been discussed in quite some detail; see for example the extensive literature on the influence of tagging species on protonated, metal, and metal oxide clusters. Tagging, in the simplest case, can lead to spectral shifts and changes in IR transition intensities.…”

“…[68] There are two alternative, elegantI Ra ction techniques that allow probing in the linear absorption regime without tagging, namely by way of laser induced reaction( LIR) [21] and laser-induced inhibition of complexg rowth (LIICG). [22,69] The influence of the nature of the tagging speciesh as been discussed in quite some detail;s ee for example the extensive literatureo nt he influenceo ft agging species on protonated, [70][71][72][73][74][75][76] metal, [77,78] and metal oxide [49] clusters. Ta gging, in the simplestc ase, can lead to spectral shifts and changes in IR transition intensities.…”

Kinetic isotope effects and how to describe them

“…One of the most successful approaches is based on optical spectroscopy, 96–100 which provides valuable benchmarks for computational studies.…”

Infrared spectroscopy of O˙− and OH− in water clusters: evidence for fast interconversion between O˙− and OH˙OH−

“…2 were calculated using a local minima approach. Therefore, the spectrum broadening arises due to the presence of different isomers; the absorption below 3000 cm À1 can be explained without invoking a mobile proton as suggested by Johnson and co-workers for protonated water clusters, 49 but this does not rule out its presence in the current experiments. Thus, the absorption intensity in the 2400-2800 cm À1 region can be attributed mainly to the signal induced by the presence of O À /OH À ion in the cluster while both ion-water and waterwater interactions are present for higher frequencies.…”