Experimental and theoretical evidence of charge transfer in weakly bound complexes of water

Abstract

We report the definitive assessment of a measurable (half a kJ/mol) charge-transfer (CT) component in the interaction of water with the noble gases. The CT is found to be strongly stereoselective and is mediated by a highly asymmetric, donor/acceptor concerted role of the two hydrogen atoms, which can in fact dictate the equilibrium geometry of the adducts. This finding may be of general relevance in explaining the known peculiar orientational features of water's interactions. By using an original method of partial integration of the change in electron density occurring upon the formation of Ng-water complexes (computed with accurate ab initio methods and basis sets), we map the local charge displacement along the whole intermolecular region and are thus able to appraise CT effects free of the inherent ambiguity of charge decomposition models. With this, it was possible to prove that a small CT (of the order of a couple of millielectrons at most) takes place from Ng to water. Most importantly, this CT correlates quantitatively with some unexpected "glory" quantum interference effects observed in high-resolution molecular-beam Ng-water scattering experiments that indicate a stronger bond than a pure van der Waals force. The energy stabilization associated with the observed CT does not exceed half a kJ mol(-1). The Ng-water CT is found to be strongly stereoselective and is mediated by a highly asymmetric, donor-acceptor concerted role of the two hydrogen atoms, which can in fact dictate the equilibrium geometry of the adducts. This finding may be of general relevance in explaining the known peculiar orientational features of water's interactions.

Charge-Displacement Analysis of the Interaction in the Ammonia–Noble Gas Complexes

“…High resolution molecular-beam scattering experiments, showing appreciable shifts in the position of quantum interference effects on the cross-section, 19 have, however, in some cases, suggested otherwise. Similar experimental findings, combined with very accurate ab initio calculations involving charge-displacement analysis, 20,21 have finally shown that even the waterÀnoble gas complexes cannot be classified as conventional noncovalent vdW systems: an appreciable (i.e., measurable) fraction of the interaction energy is due to CT. The latter was clearly demonstrated to be stereospecific, showing maximum strength for the noble gas (NG) approaching water on the hydrogen side.…”

On the Dewar–Chatt–Duncanson Model for Catalytic Gold(I) Complexes

“…The function Dq(z) was successfully introduced to study the chemical bond between gold and the noble gases [46] and also used to investigate charge transfer in weakly bound water adducts. [47,48] It defines, at each point z along a chosen axis, the amount of electron charge that, upon formation of the bond between the fragments, moves across a plane perpendicular to the axis through the point z. A positive (negative) value corresponds to electrons flowing in the direction of decreasing (increasing) z.…”

Analysis of a remarkable perpendicular band in Kr H2O with origin close to the ν1+ν3 R(0) line in H2O

“…Kr-H2O was previously studied in the gas phase in the microwave (MW) range [5] and in matrix [6]. Gas-phase collision-type experiments supported by theoretical calculations were also published [7,8], as well as pure ab initio investigations [9][10][11][12][13][14]. According to the theoretical literature, the Kr atom is oriented quite on line with one of the water O-H bonds, thus in the water plane [8,11].…”