Solvated electron extinction coefficient and oscillator strength in high temperature water.

The decadic extinction coefficient of the hydrated electron is reported for the absorption maximum from room temperature to 380 degrees C. The extinction coefficient is established by relating the transient absorption of the hydrated electrons in the presence of a scavenger to the concentration of stable product produced in the same experiment. Scavengers used in this report are SF(6,) N(2)O, and methyl viologen. The room temperature value is established as 22,500 M(-1) cm(-1), higher by 10-20% than values used over the last several decades. We demonstrate how previous workers arrived at a low value by incorrect choice of a radiolysis yield value. With this revision, the integrated oscillator strength, corrected by refractive index, is definitely (ca. 10%) larger than unity. This result is fully consistent with EPR and resonance Raman results which indicate mixing of the hydrated electron wave function with solvent electronic orbitals. Oscillator strength appears to be conserved vs temperature.

Carbonate radical formation in radiolysis of sodium carbonate and bicarbonate solutions up to 250 degrees C and the mechanism of its second order decay.

Pulse radiolysis experiments published several years ago (J. Phys. Chem. A, 2002, 106, 2430) raised the possibility that the carbonate radical formed from reaction of *OH radicals with either HCO(3)(-) or CO(3)(2-) might actually exist predominantly as a dimer form, for example, *(CO(3))(2)(3-). In this work we re-examine the data upon which this suggestion was based and find that the original data analysis is flawed. A major omission of the original analysis is the recombination reaction *OH + *CO(3)(-) --> HOOCO(2)(-). Upon reanalysis of the published data for sodium bicarbonate solutions and analysis of new transient absorption data we are able to establish the rate constant for this reaction up to 250 degrees C. The mechanism for the second-order self-recombination of the carbonate radical has never been convincingly demonstrated. From a combination of literature data and new transient absorption experiments in the 1-400 ms regime, we are able to show that the mechanism involves pre-equilibrium formation of a C(2)O(6)(2-) dimer, which dissociates to CO(2) and peroxymonocarbonate anion: *CO3(-)+*CO3(-)<-->C2O6(2-)-->CO2+O2COO(2-) *CO3(-) reacts with the product peroxymonocarbonate anion, producing a peroxymonocarbonate radical *O2COO(-), which can also recombine with the carbonate radical: *CO3(-)+CO4(2-)-->*CO4(-)+CO3(2-) *CO3(-)+CO4(-)-->C2O7(2-).

Putting atoms and molecules into chemically opened fullerenes.

We studied Ar, Kr, CO, and N(2) going into and out of a chemically opened fullerene, 1. We measured the equilibrium constant, K(eq), for the formation of X@1. K(eq) is particularly large for Ar, probably due to the large van der Waals attraction between the Ar atom and the fullerene cage. We measured rate constants and activation energies for the unimolecular reaction X@1-->X + 1 (X = Ar, CO, N(2)). The reactions show an unusually small pre-exponential factor, probably due to the loose binding of X inside the cage.

Helium entry and escape through a chemically opened window in a fullerene.

(3)He has been inserted into the cavity of an open-cage fullerene derivative close to room temperature, reaching an incorporation fraction of 0.1%. The rate of escape of (3)He from this fullerene was monitored by (3)He NMR to yield the activation barrier and to compare the size of the orifice to those of other open-cage fullerenes. The equilibrium constant was also measured.