Theoretical characterization of four distinct isomer types in hydrated-electron clusters, and proposed assignments for photoelectron spectra of water cluster anions

Water cluster anions, (H(2)O)(N)(-), are examined using mixed quantum/classical molecular dynamics based on a one-electron pseudopotential model that incorporates many-body polarization and predicts vertical electron detachment energies (VDEs) with an accuracy of ~0.1 eV. By varying the initial conditions under which the clusters are formed, we are able to identify four distinct isomer types that exhibit different size-dependent VDEs. On the basis of a strong correlation between the electron's radius of gyration and its optical absorption maximum, and extrapolating to the bulk limit (N → ∞), our analysis supports the assignment of the "isomer Ib" data series, observed in photoelectron spectra of very cold clusters, as arising from cavity-bound (H(2)O)(N)(-) cluster isomers. The "isomer I" data reported in warmer experiments are assigned to surface-bound isomers in smaller clusters, transitioning to partially embedded isomers in larger clusters. The partially embedded isomers are characterized by a partially formed solvent cavity at the cluster surface, and they are spectroscopically quite similar to internalized cavity isomers. These assignments are consistent with various experimental data, and our theoretical characterization of these isomers sheds new light on a long-standing assignment problem.     

Sequential stochastic assignment under uncertainty: estimation and convergence

This paper generalizes the sequential stochastic assignment problem, involving the assignment of workers to sequentially arriving jobs, by introducing uncertainty into the job value distribution. Three estimators are presented that address various levels of uncertainty while simultaneously improving worker assignments. Specifically, each estimator is designed to utilize the unbiased and consistent properties of the sample mean to estimate the expected job value, while suppressing high variance effects during start-up. The key contribution is that closed-loop decision policies involving past job value observations can responsively adapt to changing environments and improve the overall reward resulting from pairing workers with jobs. Examples of applications that can benefit from these results include aviation passenger screening and the real estate market, as well as applications of the stochastic knapsack problem.     

Paraffine

Ohne Zusammenfassung     

The Galois group of a radical extension of the rationals

The Galois group of the splitting field of an irreducible binomialx ^2e −a overQ is computed explicitly as a full subgroup of the holomorph of the cyclic group of order 2 ^e . The general casex ⁿ −a is also effectively computed.     

Structure of trans-W(C0)4(CNC6H11)(CS) and a correlation of ν(cs) frequencies with CS bond distances in metal thiocarbonyl complexes

An X-ray structural investigation of $\text{trans}$-W(C0)₄(CNC₆H₁₁)(CS) shows that the Wz.bnd;C bond distances to the 3 isoelectronic ligands increase in the order: WCS(1.944Å) < WCO(2.0645Å, average) < WCNC₆H₁(2.158Å). Using data from this molecule as well as results from other thiocarbonyl complexes reported in the literature, an excellent correlation of low ν(CS) frequencies with long CS bond distances is observed, a trend which supports current bonding theories for thiocarbonyl complexes.