Infrared Spectroscopy and Anharmonic Vibrational Analysis of (H₂O–Kr_n)⁺ (n = 1–3): Hemibond Formation of the Water Radical Cation

Abstract

The hemibond is a nonclassical covalent bond formed between a radical (cation) and a closed shell molecule. The hemibond formation ability of water has attracted great interest, concerning its role in ionization of water. While many computational studies on the water hemibond have been performed, clear experimental evidence has been hardly reported because the hydrogen bond formation overwhelms the hemibond formation. In the present study, infrared photodissociation spectroscopy is applied to (H2O–Kr n )+ (n = 1–3) radical cation clusters. The observed spectra of (H2O–Kr n )+ are well reproduced by the anharmonic vibrational simulations based on the hemibonded isomer structures. The firm evidence of the hemibond formation ability of water is revealed.

Microsolvation of H2O+, H3O+, and CH3OH2+ by He in a cryogenic ion trap: structure of solvation shells

“…This is in contrast to H 2 O + Rg n with the larger Rg atoms Ar and Kr, which have been grown and studied up to n = 14 and 3, respectively. 93,94 Fig. 6 summarizes the predicted evolution of the OH stretch and H 2 O bend frequencies n 1-3 as a function of cluster size for the size range n = 0-5 as basis for future IRPD spectroscopy and includes the available experimental data for n = 0 and 1 (Table S2 in ESI †).…”

Infrared spectroscopy of [H2O–Xn]+(n= 1–3, X = N2, CO2, CO, and N2O) radical cation clusters: competition between hydrogen bond and hemibond formation of the water radical cation

“…Structures of the [H 2 O–X] + (X = He, Ne, Ar, Kr, CO 2 , N 2 O, and H 2 O) radical cation clusters have been studied by infrared (IR) spectroscopy in the gas phase. 21–31 Two structural motifs are confirmed: hydrogen bond (H-bond) and hemibond. The H-bonded type has a structure in which X is H-bonded to one of the OH groups of H 2 O + (HOH⋯X).…”

“…Recently, however, it was found that the hemibond formation is favored over the H-bond formation in the cases of X = N 2 O and Kr. 30,31 Here, a question arises; what factors govern the competition between H-bond and hemibond formation.…”

Infrared Spectroscopy of (Benzene–H2S–Xn)+, X = H2O (n = 1 and 2) and CH3OH (n = 1), Radical Cation Clusters: Microsolvation Effects on the S−π Hemibond

“…The main experimental approach to hemibond formation has been observations of broad (σ, σ*) transitions of samples in the condensed phase. , On the other hand, spectroscopic and mass spectrometric studies of hemibonds in gas phase clusters have increasingly been reported. ,,− Gas phase cluster studies enable us to explore microscopic details of hemibonds in model systems. One of the central issues in such cluster studies is the competition between hemibond and hydrogen bond (or proton transfer) with microsolvation by protic solvent molecules, such as water, methanol, and ammonia. , It has been demonstrated that an S∴S hemibond can be broken by microsolvation with a few molecules.…”