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The potential-energy surface features involved in the [OCS+C2H2]+ reaction system allow a metastable enroute to reaction to be trapped. The absolute photodissociation spectrum of this trapped metastable [OCS·C2H2]+ cluster ion has been measured in the wavelength region between 375 and 735 nm using a coaxial-laser–triple-quadrupole ion-beam apparatus. The photodissociation spectrum consists of at least three broad overlapping profiles, and OCS+, C2H+2, and C2H2S+ are the observed ionic photoproducts. The spectrum is interpreted in terms of transitions to excited charge-transfer states which are repulsive and to a dissociative transition which is localized on the perturbed OCS+ moiety. The C2H+2 fragment becomes detectable within sensitivity limits at 1.69 eV, yielding an upper limit estimate of 1.46 eV (+0.15/-0.23 eV) for the cluster bond dissociation energy. The C2H2S+ product is only observable at photon energies greater than 2.74 eV and is considered to be the product of a photoinitiated intracluster ion–molecule reaction. [ABSTRACT FROM AUTHOR]

Cuticular waxes represent the first and, in most cases, the limiting barrier for foliar uptake of pesticides from solution. Sorption of pesticides in reconstituted cuticular wax (wax/water partition coefficients) of Chenopodium album L. and in isolated cuticular membranes (cuticle/water partition coefficients) of Prunus laurocerasus L. was determined. Diffusion coefficients of pesticides in reconstituted cuticular wax of C. album leaves were size-dependent, increasing with increasing molar volume. In the presence of alcohol ethoxylates, diffusion coefficients were enhanced by up to two orders of magnitude, and size selectivity was significantly decreased. The accelerating effect and the decrease in size selectivity were attributed to plasticisation of the cuticular wax by the alcohol ethoxylates increasing the fluidity in the wax. A free volume model adopted from polymer science was successfully applied to predict diffusion coefficients of pesticides on the basis of the transport properties of the wax (size selectivity and crystaffinity), the molar volume of the diffusing compound and the accelerator concentration in the wax. [ABSTRACT FROM AUTHOR]

The surface properties of the plant cuticle play a crucial role in plant-pathogen interactions and the retention and penetration of agriculturally important chemicals. This paper describes the use of X-ray photoelectron spectroscopy (XPS), time-of-flight secondary-ion mass spectrometry (ToF-SIMS), tapping-mode atomic force microscopy (TM-AFM) and scanning electron microscopy (SEM) to determine surface-specific chemical and material properties of the adaxial surface ofPrunus laurocerasusL. leaves. XPS data, derived from the uppermost few nanometres (<10 nm) of the leaf surface, were consistent with the wax components and functionality known to be present within the waxes. ToF-SIMS provided molecular speciation from the outermost monolayer of the leaf surface, indicating the importance of a family of acetates with chain lengths ranging from C20 to C34. The presence of alkanes with C29 and C31 chain lengths was also confirmed. SEM and TM-AFM topography images revealed a textured granular surface, while simultaneously recorded AFM phase images revealed heterogeneous material properties at the nanoscale. The relevance of these data to plant cuticle development, allelochemistry and agrochemical delivery is discussed. [ABSTRACT FROM AUTHOR]