Photodissociation of a Surface-Active Species at a Liquid Surface: A Study by Time-of-Flight Spectroscopy

Citations Over Time

Abstract

The photochemistry at a gas−liquid interface was investigated by time-of-flight/quadrupole mass spectroscopy (TOF/QMS). A thin liquid film of 4-iodobenzoic acid (IBA), dissolved in glycerol, was irradiated with nanosecond laser pulses at 275 nm. Atomic and molecular iodine were the only photoproducts leaving the liquid after a low-fluence laser pulse (99%). In contrast, I atoms desorbing from IBA/glycerol are hyperthermal (Ttrans = 480 K) and originate almost exclusively from the topmost molecular layer (1 nm). TOF measurements with a fast chopper wheel in front of the surface provide the time-dependent desorption flux from the surface and confirm that the contribution from deeper layers in the alkyl iodide solution is much larger than in the aryl iodide solution. Model calculations predict the behavior of the two solutions correctly if differences in caging of the geminate pair, diffusion coefficients of the free radicals, and the set of bulk radical reactions in the two solutions are taken into account. The hyperthermal energies of the ejected I atoms from the IBA solution are discussed in terms of the surface orientation of excited IBA molecules. The dependence of the TOF spectra on laser power and IBA concentration is interpreted by a surface excess of IBA. The result is compared to temperature-dependent surface tension measurements of IBA solutions in glycerol and water. The response of the surface tension to an accumulation of IBA at the surface is very weak.

Related Papers

• → Thermodynamic effects of orientational order in chain-molecule mixtures. Part 2.—Temperature-dependence of heats of mixing of branched and normal alkane mixtures(1974)47 cited
• → Methylgroup interaction of hydrocarbon stationary phases and hydrocarbon solutes(1969)18 cited
• → Vapor−Liquid Equilibrium for Mixtures of Hexane and Squalane at Temperatures from 469.8 K to 623.3 K(1997)11 cited
• → Use of linear and branched-chain paraffinic liquid phases as non-polar reference materials in gas chromatography(1979)8 cited
• → The Effect of Aromatic Hydrocarbons on the Oxidation Stability of Squalane (Part 2)(1977)