Gas phase infrared multiple-photon dissociation spectra of methanol, ethanol and propanol proton-bound dimers, protonated propanol and the propanol/water proton-bound dimer

• Published in: Physical chemistry chemical physics : PCCP 2006-01, Vol.8 (8), p.955-966
• Main Authors: FRIDGEN, Travis D, MACALEESE, Luke, MCMABON, Terry B, LEMAIRE, Joel, MAITRE, Philippe
• Format: Article
• Language: English
• Subjects: 1-Propanol - chemistry; Alcohols - chemistry; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Chemical Physics; Chemistry; Density-functional theory; Dimerization; Electronic structure of atoms, molecules and their ions: theory; Ethanol - chemistry; Exact sciences and technology; Gases; General and physical chemistry; Hydrogen Bonding; Methanol - chemistry; Models, Molecular; Photons; Physics; Protons; Spectrophotometry, Infrared - methods; Thermodynamics; Water - chemistry
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/b516661f

The infrared multiphoton dissociation (IRMPD) spectra of three homogenous proton-bound dimers are presented and the major features are assigned based on comparisons with the neutral alcohol and with density functional theory calculations. As well, the IRMPD spectra of protonated propanol and the propanol/water proton-bound dimer (or singly hydrated protonated propanol) are presented and analysed. Two primary IRMPD photoproducts were observed for each of the alcohol proton bound dimers and were found to vary with the frequency of the radiation impinging upon the ions. For example, when the proton-bound dimer absorbs weakly a larger amount of S(N)2 product, protonated ether and water, are observed. When the proton-bound dimer absorbs more strongly, an increase in the simple dissociation product, protonated alcohol and neutral alcohol, is observed. With the aid of RRKM calculations this frequency dependence of the branching ratio is explained by assuming that photon absorption is faster than dissociation for these species and that only a few photons extra are necessary to make the higher-energy dissociation channel (simple cleavage) competitive with the lower energy (S(N)2) reaction channel.