The k-moment method for the narrow band modeling of radiative properties of nonuniform gaseous media

Moments of the absorption coefficient distribution function are used for the derivation of statistical narrow band (SNB) model parameters of nonuniform optical paths in gases. The approach yields approximations for the path-averaged first- and second-order k-moments from which equivalent SNB parameters are determined in the frame of the Malkmus model. The approach is assessed through comparisons with LBL data. The nonuniform approximation is shown to enable the computation of transmissivities and radiation intensities with accuracy similar to or higher than those achieved by the Curtis-Godson one.     

Optical properties of gas-phase tryptophan-silver cations: charge transfer from the indole ring to the silver atom.

We present a joint experimental and theoretical investigation of the electronic excitation spectra of the tryptophan-silver complex. The photodissociation spectrum of gas-phase [Trp-Ag]+ was measured from 215 to 330 nm using a quadrupole ion trap coupled to an optical parametric-oscillator laser. The calculated time-dependent density functional theory (TD-DFT) absorption spectra for different prototypes of structures are presented. Low-energy transitions that are experimentally observed are only calculated for the charge-solvation (CS) structures. These transitions are a signature of the metal-pi interaction in [Trp-Ag]+. The recorded spectrum is compared to a Boltzmann average of the absorption spectrum obtained from direct molecular dynamics (MD) simulations involving simultaneous transitions to excited states based on semiempirical configuration interaction (CI) calculations. The results demonstrate that charge transfer can be photoinduced from the indole ring to the silver atom.     

Assessment of time-dependent density functional theory for predicting excitation energies of bichromophoric peptides: case of tryptophan-phenylalanine

The ability of applied time-dependent density functional theory to predict the near-ultraviolet absorption spectrum of bichomophoric peptides in the gas phase has been tested by calculating the vertical excitation energies of the Tryptophan-Phenylalanine (Trp-Phe) dipeptide. We show that the contamination of the low-frequency part of the spectrum by spurious charge-transfer excitations depends both on the conformation of the peptide chain and the exchange-correlation approximation. For the most stable structure investigated, a hybrid density functional appears to eliminate a large proportion of the spurious states.     

Pd3Sn8Bi6]4-: a 14-vertex Sn/Bi cluster embedding a Pd3 triangle

The endohedral cluster anion [Pd(3)Sn(8)Bi(6)](4-) crystallizes as its K([2.2.2]crypt)(+) salt 1 upon reaction of [K([2.2.2]crypt)](2)[Sn(2)Bi(2)]·en and Pd(dppe)(2) in 1,2-diaminoethane (en)/toluene and incorporates a complete Pd(3) triangular cluster within a medium-size 14-vertex cage of Sn and Bi atoms. 1 was characterized by a combination of single crystal diffraction, ESI mass spectrometry, elemental analysis, and magnetic measurements. According to quantum chemical investigations, the Pd(3) triangle interacts only weakly with the Sn/Bi cluster shell despite the relatively small cavity inside the cage.     

Record ferromagnetic exchange through cyanide and elucidation of the magnetic phase diagram for a Cu(II)Re(IV)(CN)2 chain compound

Reaction of the high-magnetic anisotropy building unit [ReCl(4)(CN)(2)](2-) with [Cu(MeCN)(6)](2+) and hydrotris(pyrazol-1-yl)borate (Tp(-)) affords the zigzag chain compound (Bu(4)N)[TpCuReCl(4)(CN)(2)]. Dc magnetic susceptibility measurements reveal the presence of ferromagnetic exchange coupling between Re(IV) and Cu(II) centers along each chain and a fit to the data gives an exchange constant of J/k(B) = +41 K (+29 cm(-1)), representing the strongest ferromagnetic coupling yet observed through cyanide. Below 11.4 K and at applied fields of less than 3600 Oe, the compound undergoes a phase transition to an antiferromagnetic ground state, stemming from weak π-π interchain interactions of strength J(⊥)/k(B) = -1.7 K (-1.2 cm(-1)). This metamagnetic behavior is fully elucidated using both experimental and theoretical methods. In addition, theoretical modeling provides a detailed determination of the local anisotropy tensors corresponding to the [ReCl(4)(CN)(2)](2-) units and demonstrates that the zigzag arrangement of the Re(IV) centers significantly reduces the effective anisotropy of the chain. These results demonstrate the utility of the Re(IV)-CN-Cu(II) linkage and the importance of anisotropic spin orientation in designing strongly coupled systems, which will aid in both the realization of single-chain magnets with higher relaxation barriers and in the construction of high-dimensional cyano-bridged materials exhibiting higher ordering temperatures.