Experimental verification of a zero-dimensional model of the kinetics of XeCl* discharges by XeCl*(B)-, XeCl*(C)-, and Xe2Cl*-density measurements

Absolutely calibrated emission spectroscopy has been used to determine the particle number densities of XeCl^*(B), XeCl^*(C), and Xe₂Cl^* in a small scale Ne/Xe/HCl discharge with well-defined current and voltage pulses for a wide range of parameters. The measured particle number densities could be reproduced quite well by numerical model calculations using the rate-coefficient values of Quiñones et al. [1] for the quenching of XeCl^*(B,C) by Ne, Xe, and 2Xe, but 3.0 × 10^–31 cm⁶/s for the formation of Xe₂Cl^* by (Ne + Xe)-quenching. For the electron quenching, we recommend a rate coefficient value of 3.2 × 10^–8 cm³/s. From the equilibrium ratio of the particle number densities of XeCl^*(C) and XeCl^*(B), the energy separation between these states has been estimated to be 72 ± 33 cm^–1 with the B state placed above the C state.     

More characterizations of triangulated graphs

New characterizations of triangulated and cotriangulated graphs are presented. Cotriangulated graphs form a natural subclass of the class of strongly perfect graphs, and they are also characterized in terms of the shellability of some associated collection of sets. Finally, the notion of stability function of a graph is introduced, and it is proved that a graph is triangulated if and only if the polynomial representing its stability function has all its coefficients equal to 0, +1 or ?1.     

Derivatives of 1-azabicyelo[4.3.1]decane

1-Azabicyclo[4.3.1]decan-3-one has been synthesized via Dieckmann condensation and converted to the corresponding hydroxy and chloro derivatives.     

Single-molecule studies of a model fluorenone.

Single-molecule fluorescence measurements of 2,7-bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) reveal narrow emission spectra concentrated around 540 nm, with weak emission at longer wavelengths. The wide scattering of emission-maximum wavelengths is attributed to varying molecular environments, with dimers or higher-order aggregates contributing to the low-energy emission. This spectral distribution indicates that emission from monomers of this model fluorenone is mostly green, which is consistent with contaminant emission (g-bands) often observed in fluorene- and polyfluorene-based organic light emitting diode (OLED) devices. A histogram of center wavelengths from 118 single-molecule spectra shows good agreement with the green emission previously observed in thermally stressed 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV). Whereas bulk OFPV exhibits blue fluorescence at about 480 nm, OFOPV bulk thin film measurements reveal red luminescence shifted to 630 nm. This unexpected peak position for bulk OFOPV shifts to higher energies (ca. 540 nm) upon dilution in a solid-state matrix, suggesting that the bulk red emission finds its origins in interactions between fluorenone molecules. Explanations for this red emission include aggregate or excimer formation or intermolecular energy transfer between fluorenone molecules.     

IR study of cross-strand coupling in a beta-hairpin peptide using isotopic labels

Model beta-hairpin peptides can be used to develop understanding of fundamental elements of beta-sheet secondary structure formation and stability. We have studied two 13C-labeled variants of a beta-hairpin peptide modified from a design originally proposed by Gellman: Arg-Tyr-Val-Glu-Val-Aib-Gly-Lys-Lys-Ile-Leu-Gln. (In this peptide, the two italicized residues form a beta-turn, while 13C-labels are on the amide C=O of Val3, Lys8 in HBG-L and Val3, Ile10 in HBG-S.) Both these peptides are labeled on opposite strands of the hairpin, but differ in the labeling pattern. One (HBG-L) forms a large (14-atom) H-bonded ring of labeled C=Os, while the other (HBG-S) forms a small (10-atom) H-bonded ring. These impact the amide I infrared spectra, with HBG-L having a 13C frequency and intensity higher than that of HBG-S, in good agreement with our spectral simulations based on quantum mechanically derived force fields. The thermal behavior of both peptides yields a broad thermal transition and lacks an isosbestic point. The 13C band for HBG-L has the largest intensity change with temperature, distinct from the 12C change and the HBG-S 13C change.     

Synthèses dans la série des bis-indéno-fluorènes IV [1] Hydroxy-8-dihydro-9, 15-7H-bis-indéno[2, 1-b;2′, 1′-g]fluorène

8-Hydroxy-9, 15-dihydro-7H-diindeno [2, 1-b;2′, 1′-g] fluorene, a derivative of a new mono-angular diindenofluorene system, has been synthesised in 6 steps (overall yield 42%) starting from 9-oxo-fluorene-1-carbaldehyde and acetophenone. The corresponding hydrocarbon could not be obtained by reductive scission of the hydroxyl group.     

Negative ions of ethylene sulfite

The formation of negative ions in molecular beams of ethylene sulfite (ES, alternately called glycol sulfite or ethylene glycol, C(2)H(4)SO(3)) molecules has been studied using both Rydberg electron transfer (RET) and free electron attachment methods. RET experiments with jet-cooled ES show an unexpected broad profile of anion formation as a function of the effective quantum number (n(*)) of the excited rubidium atoms, with peaks at n(max)(*) approximately 13.5 and 16.8. The peak at n(max)(*) approximately 16.8 corresponds to an expected dipole-bound anion with an electron binding energy of 8.5 meV. It is speculated that the peak at n(max)(*) approximately 13.5 derives from the formation of a distorted C(2)H(4)SO(3)(-) ion. We suggest that quasifree electron attachment promotes the breaking of one ring bond giving a long-lived acyclic anion and term this process incomplete dissociative electron attachment. Theoretical calculations of plausible ionic structures are presented and discussed. Electron beam studies of ES reveal the presence of multiple dissociative attachment channels, with the dominant fragment, SO(2)(-), peaking at 1.3 eV and much weaker signals due to SO(3)(-), SO(-), and (ES-H)(-) peaking at 1.5, 1.7, and 0.9 eV, respectively. All of these products appear to originate from a broad temporary negative ion resonance centered at approximately 1.4 eV.