Photoelectron spectra and angular distribution in reson three-photon ionization of atomic iron: J dependence

Kenetic energies and angular distributions of photoelectrons emitted by three-photon ionization fo atomic iron through two-photon resonant state e⁷D_J and e⁵ D_J, were measured, by using visible lasers. J-resolved photoelectron bands attributab to the a⁶D_J and a⁴F_j ionic states are reported.     

Standard molar enthalpy of formation of CH<Subscript>3</Subscript>(CH<Subscript>3</Subscript>SCH<Subscript>2</Subscript>)SO,methyl methylthiomethyl sulfoxide

Summary The standard molar enthalpy of formation of methyl methylthiomethyl sulfoxide, CH₃(CH₃SCH₂)SO, at T=298.15 K in the liquid state was determined to be -199.4±1.5 kJ mol^-1 by means of oxygen rotating-bomb combustion calorimetry.     

Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH_2.76O_3.89 (Adams' catalyst) and dehydrated oxide PtO_2.52 at T=298.15 K were determined to be -519.6±1.0 and -101.3 ±5.2 kJ mol^-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO₂ was estimated to be -80 kJ mol^-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol^-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric. This revised version was published online in August 2006 with corrections to the Cover Date.     

Micro-combustion Calorimetry Aiming At 1 mg Samples

A micro-combustion calorimeter was developed. The small energy equivalent (ca. 68 JK_–1) of this calorimeter makes it possible to measure combustion energies of very small samples. The energy equivalent was determined by burning 2 mg of benzoic acid. The standard deviation of the mean energy equivalent was reduced to 0.014% in 5 experiments. The standard massic energy of combustion of salicylic acid and the standard deviation of the mean were determined to be –21871±5 J g_–1, which agrees well with the literature values. The standard molar enthalpy of formation of salicylic acid was derived as –591.2±1.7 kJ mol_–1.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mixing schemes in a urea-H2O system: a differential approach in solution thermodynamics

The excess partial molar enthalpies of urea (UR), H U R (E ), were experimentally determined in UR-H 2O at 25 degrees C. The H U R (E ) data were determined accurately and in small increments in the mole fraction of UR, x U R , up to x U R approximately 0.22. Hence it was possible to evaluate one more x U R -derivative graphically without resorting to any fitting function, and the model-free UR-UR enthalpic interaction, H U R- U R (E ), was calculated. Using previous data for the excess chemical potential, mu U R (E ), the entropy analogue, S U R- U R (E ), was also calculated. The x U R -dependences of both H U R- U R (E ) and S U R- U R (E ) indicate that there is a boundary at x U R approximately 0.09 at which the aggregation nature of urea changes. From the results of our earlier works, we suggest that a few UR molecules aggregate at x U R approximately 0.09, while the integrity of H 2O is retained at least up to x U R approximately 0.20. Together with the findings from our previous studies, we suggest that in the concentration range x U R < 0.22, UR or its aggregate form hydrogen bonds to the H 2O network, reducing the degree of fluctuation characteristic to liquid H 2O. However, up to at least x U R = 0.20 the hydrogen bond network remains intact. Above x U R approximately 0.22, the integrity of H 2O is likely be lost. Thus, in discussing the effect of urea on H 2O and in relating it to the structure and function of biopolymers in aqueous solutions, the concentration region in question must be specified.