Vibrational predissociation spectra of the Ar-tagged [CH₄· H₃O⁺] binary complex: spectroscopic signature of hydrogen bonding to an alkane

Abstract

2010) Vibrational predissociation spectra of the Ar-tagged [CH 4 · H 3 O + ] binary complex: spectroscopic signature of hydrogen bonding to an alkane, Vibrational predissociation spectra of the Ar-tagged [H 3 O þ Á X], X ¼ CH 4 , CD 4 , N 2 , and Ar complexes are analysed to explore the hydrogen bonding acceptor properties of an alkane. The observed red shift in the OH stretching transition of the donor is found to be significantly smaller than anticipated by the previously reported trend in this value with the proton affinity of the acceptor [Science 316, 249 (2007)] [1]. Specifically, the alkane-induced red shift of the OH stretching frequency is less than that caused by the conventional proton acceptor, N 2 , even though the latter is a weaker base than methane. The origin of this effect is discussed in the context of the structures of the complexes and the molecular rearrangements required for complete proton transfer to hydrocarbons as opposed to the situation in conventional H-bond acceptors.

Vibrational manifestations of strong non-Condon effects in the H3O+·X3 (X = Ar, N2, CH4, H2O) complexes: A possible explanation for the intensity in the “association band” in the vibrational spectrum of water

“…The features in this region have been discussed at length in earlier work by us and by Duncan and co-workers. 2,21,53 Qualitatively, the systematic blue-shift of the a-band with increasing strength of the solvent interaction is consistent with the expected behavior of the bend-rotation combination band. Indeed, the calculated harmonic spectra of these complexes, as shown in the right columns of Table 1, follow the same trends as the spacing between the a-band and n HOH .…”

“…Here, the evolution of the bands as the proton affinity of the ligands is varied is informative, as the HOH bending transition in the H 3 O + core ion (labeled n HOH ) is observed to systematically blue-shift through the series (green line), while at the same time the symmetric and asymmetric OH stretches (highlighted in blue), which account for the dominant band in the mid-IR at B3300 cm À1 in H 3 O + ÁAr 3 (Fig.4b) dramatically red-shift down to B2650 cm À1 in H 3 O + Á(H 2 O) 3 ÁAr (Fig.4e). The features in this region have been discussed at length in earlier work by us and by Duncan and co-workers 2,21,53.…”

Infrared photodissociation spectroscopy of H+(H2O)6·Mm (M = Ne, Ar, Kr, Xe, H2, N2, and CH4): messenger-dependent balance between H3O+ and H5O2+ core isomers

“…However, to the best of our knowledge, systematic studies of messenger-dependent isomer-selectivity have never been reported. Although IR spectroscopy has been reported for phenol + ÁM m , 58 H 2 O + ÁM m , [53][54][55]57 H 3 O + ÁM m , 9,10,65,66 21,22 (M = rare gas, H 2 , N 2 , CH 4 ), and so on, isomerization in the moieties of interest cannot be expected in these relatively rigid systems.…”

Gas-Phase Ion Chemistry of the Noble Gases: Recent Advances and Future Perspectives

“…The noble gas-tagging technique 109,110 mentioned in the previous paragraph has recently been employed to investigate the IR absorptions of various non-metal cations. [136][137][138][139][140][141][142][143][144][145] It is first of interest to mention the "Eigen" (H 3 O + ) and the "Zundel" (H 2 O-H-OH 2 + ) cations, the two limiting forms of proton accommodation in water. The relative weight of these two ions essentially depends on the number of solvating water molecules and this stimulates considerable interest for the structure and stability of H + (H 2 O) n clusters of variable size.…”

“…The experimental results are invariably supported by ab initio or DFT calculations and detailed accounts of exemplary results had already been reported in review articles. 109,146,149 At variance with the above-mentioned applications of the Ng-tagging technique, [136][137][138][139][140][141][142][143][144][145] more emphasis is placed in these studies on the ion-ligand interactions and bonding motifs. A good recent illustrative case is the complexes of Ar with protonated benzaldehyde (BZH + ).…”