Structural Isomerism and Competitive Proton Solvation between Methanol and Water in H⁺(CH₃OH)_m(H₂O)_n, m + n = 4

Abstract

Competitive solvation of the excess proton in protonated mixed methanol−water clusters [H+(CH3OH) m (H2O) n , m + n = 4] has been characterized by vibrational predissociation spectroscopy in combination with density functional theory calculations. The solvation topology of the clusters can be classified as (1) the closed shell, in which a hydronium ion H3O+ is fully solvated by three neutral molecules forming a complete solvation shell, and (2) the open chain, where the excess proton is tugged between two mixed subunits in a linear chain. The existence of these two types of isomer is verified from a close examination of the characteristic free-OH and hydrogen-bonded-OH stretching modes in the spectra. It is found that sequential replacement of the water molecule in H+(H2O)4 by methanol redistributes the population between the closed-shell and the open-chain isomers. While the excess proton is preferentially taken by methanol (instead of water) in the chain configuration, it can be either localized as CH3OH2 + or delocalized as CH3OH···H+···CH3OH at m ≥ 2, depending sensitively on the number of the methanol molecules and the symmetry of the cluster isomers. In contrast to that of NH4 +(NH3) m (H2O) n , m + n = 4, previously studied, this work provides a clear picture of competitive solvation of a charge between the constituent solvent molecules within a cluster.

Electron-driven ionization of large methanol clusters in helium nanodroplets

“…Evidence for this comes not only from mass spectrometry, but also from the infrared spectroscopy of small protonated mixed methanolwater clusters. 19 Guided by earlier work on neutral and ionic clusters of both water and methanol, where structures derived from hydrogen-bonded five-membered rings could account for Once the possibility of the DME forming a hydrogen bond with any of the solvent molecules is removed, as it is for the closed ring structures, the DME becomes easier to eject from the ion.…”

“…[18][19][20] Helium nanodroplets provide an alternative medium for exploring ion-molecule chemistry in molecular clusters. 21 These droplets allow clusters to be grown in a cold environment (ca.…”

First principle study on the structure of H+(H2O)6

“…The structure of protonated water cluster have been the subject of recent experimental studies [1][2][3][4][5][6] . In this work, we have chosen to investigate the structure of H + (H 2 O) 6 by examining the low-lying minima with first principle methods for several reasons.…”

Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase

“…Several ways of overcoming the number density restriction have now been developed, each based upon the coupling of ionisation techniques such as electro-spray (ESI), or matrix assisted laser desorption (MALDI), [17][18][19][20][21][22][23][24][25], or electron impact, [26][27][28][29][30][31][32][33] or electrical discharge [34][35][36][37][38] with mass filtering, and cumulative storage in ion traps to enhance their number densities. Their molecular structures have been probed through resonant single, or multiphoton infrared photodissociation spectroscopy.…”