The value of the proton hydration free energy, ΔGhyd(H+), has been quoted in the literature to be from −252.6 to −262.5 kcal/mol. In this article, we present a theoretical model for calculating the hydration free energy of ions in aqueous solvent and use this model to calculate the proton hydration free energy, ΔGhyd(H+), in an effort to resolve the uncertainty concerning its exact value. In the model we define ΔGhyd(H+) as the free energy change associated with the following process: ΔG[H+(gas)+H2nOn(aq)→H+(H2nOn)(aq)], where the solvent is represented by a neutral n-water cluster embedded in a dielectric continuum and the solvated proton is represented by a protonated n-water cluster also in the continuum. All solvated species are treated as quantum mechanical solutes coupled to a dielectric continuum using a self consistent reaction field cycle. We investigated the behavior of ΔGhyd(H+) as the number of explicit waters of hydration is increased from n=1 to n=6. As n increases from 1 to 3, the hydration free energy decreases dramatically. However, for n=4–6 the hydration free energy maintains a relatively constant value of −262.23 kcal/mol. These results indicate that the first hydration shell of the proton is composed of at least four water molecules. The constant value of the hydration free energy for n⩾4 strongly suggests that the proton hydration free energy is at the far lower end of the range of values that have been proposed in the literature.

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Recent developments in time-resolved photoacoustic calorimetry (PAC) are discussed. An equation is derived relating the amplitude of the maximum photoacoustic signal to parameters of a photoacoustic cell, to physical properties of the solvents, and to the energy deposited as heat. The equation is validated by a series of scaling experiments: it correctly correlates the dependence of the PAC signal on cell thickness, on energy deposition, and on solvent properties. The dominant sources of background signal have been determined and the background signal reduced substantially relative to previous work. It is now possible to measure energies and lifetimes of transients in solutions with optical densities as low as ∼5×10−4. Data are presented for the energy of 2-cyclopentenone triplet, a transient for which interpretable PAC measurements were previously not possible. Its triplet energy is 73.1±1.1 kcal/mole. With reduced background and a faster digital storage oscilloscope, a quite short transient lifetime, 7.53±0.2 ns, and a triplet energy of 51.0±2.1 kcal/mol have been measured for 1,1-bis-(p-bromophenyl)ethene. The lifetime agrees very well with that determined by kinetic absorption spectroscopy and the triplet energy agrees with expectation based on the unsubstituted 1,1-diphenylethene.

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Format and instructional revisions were made in the TRF, a previously reported school adjustment measure, to extend its diagnostic, prescriptive, and empirical utility. Factor analyses of school adjustment ratings on the revised CARS with a normative sample of "healthy" primary graders demonstrated that while the revisions maintained the scale's original three-factor structure, they increased specific item factor loadings and accounted scale variance. To extend the screening utility of the proposed measure, normative and parametric comparisons are reported describing adjustment ratings for sex, age, and city/country subgroups. Comparisons of children who are or are not referred to a secondary prevention program provide evidence of the CARS discriminative validity and screening potential.