Transient ESR nutation signals in excited aromatic triplet states

Transient ESR nutation signals following laser pulse excitation are analyzed for the case of the photoexcited triplet state of acridine in a molecular crystal matrix. Essential features, in particular the short rise-time (< 10^?7) of the signals, can be related to the inhomogeneous nature of the ESR linewidth. Applications are discussed.     

Catalyst- and organic solvent-free synthesis of thioacids in water

Thioacids and thioamino acids were synthesized in excellent yields from readily available acyl benzotriazoles and sodium hydrosulfide in water at room temperature. The new methodology features mild reaction conditions, high yields, short reaction times, and does not involve the use of organic solvents or bases. The reaction is eco-friendly, and the workup procedure is simple and does not require chromatographic separation.     

Electrical conduction in semiconducting NbO2 at hydrostatic pressures up to 6000 atm

We have measured the dc resistance, R, of n-type NbO₂ single crystals in the semiconducting, distorted rutile-structured phase at temperatures from T = 196 K to 410 K using hydrostatic pressures, P, from one to 6000 atm. The resistivity, divided by the temperature, increases exponentially with $\text{1}\text{T}$ and the resistance increases linearly with $\text{P}\text{T}$ at different rates along the a- and c-axes. We find that conduction is due to thermally-activated, adiabatic hopping of small polarons and obtain values and pressure dependences for the vibrational frequency and polaronic energies involved. A discussion of our results is given.     

Energy ordering of the B and C states in XeCl,XeBr, and KrCl,from temperature dependence of emission spectra

Inert-gas halide emission spectra from a Tesla discharge are studied as a function of pressure and temperature. From the temperature dependence of the infinite pressure ratio of broad-band (C → A and B → A) emission to B → X emission, the energy separations, T_eC - T_eB, are found to be ?130 cm^?1 (XeCl), ?80 cm^?1 (XeBr) and 375 cm^?1 (KrCl). Estimates of the (C → A)/(B → X) spontaneous emission branching ratios agree well with theoretical predictions.     

Excitation profiles of resonance raman spectra in condensed media

A simple model, obtained by reducing a multimode system to a simple coordinate, is proposed to explain the broadening of RRS in liquid or solid media. It is shown that the coherent excitation of the near continuous background of low-frequency modes can cause homogeneous broadening of RRS profiles. The model is applied to the excitation profile of β-carotene.     

A general,enantioselective synthesis of 2-substituted thiomorpholines and thiomorpholine 1,1-dioxides

In the course of our drug discovery programs, we had need to access chiral, 2-substituted thiomorpholines and their oxidized congeners, thiomorpholine 1,1-dioxides. Here, we disclose a high-yielding, general protocol for the enantioselective synthesis of C2-functionalized thiomorpholines and thiomorpholine 1,1-dioxides.     

Thermal properties of xenon adsorbed on graphite

We report theoretical results for dynamical and thermodynamic properties of the bare graphite (0001) surface, and with a physisorbed monolayer of xenon. The surface vibrations of graphite are less pronounced than those in more isotropic crystals. The surface-excess specific heat of the bare surface peaks at 45 K, that of the xenon at 13.5 K.     

Kinetische und mechanistische untersuchungen von Übergangsmetall-komplex-reaktionen : III. Abhängigkeit des gleichgewichts der addition von tributylphosphan an pentacarbonyl(arylmethoxycarben)wolfram vom substituenten am ring

The reaction of pentacarbonyl(arylmethoxycarbene)tungsten, (CO)₅W[C(OCH₃(p-C₆H₄R)] [R = OCH₃ (a), CH₃ (b), H (c), Br (d), CF₃ (e)], with tributylphosphane at low temperatures results in a reversible addition of the phosphane to the carbene carbon atom. The addition—dissoziation equilibrium is not only dependent on the temperature but also to a strong degree on the nature of the substituent R. ΔG, ΔH and the equilibrium constant K increase in the series from R = OCH₃ to R = CF₃. With the exception of R = OCH₃ the substituents b to e form an isentropic class. For all substituents (a to e) a linear dependency from Jaffés σ-constants was observed for ΔH. Good linear correlation for the substituents b to e was also found for log K and σ as well as for log K and the CO-force constants k_cis and k_trans.     

Quasiclassical trajectory study of colinear Cl− + HBr → HCl + Br−

Energy distributions in the products of the ion-molecule reaction Cl^? + HBr → HC1 + Br^? have been studied using quasiclassical trajectories on a semi-empirical collinear potential energy surface. Vibrational energy is favored in the products. While some trajectories are long-lived, the kinematic factor of the light central atom prevents effective energy redistribution.     

On the ordering of the ionization energies in N2: A MC SCF study of near-degeneracy effects

Single configuration SCF wavefunctions yield poor results for the order and relative energies of low-lying icnic states of N₂. A multi-configurational SCF (MC SCF) model which takes account of the near degeneracy of a small number of strongly and weakly occupied orbitals corrects the errors of the SCF approach. MC SCF results for N₂ predict the correct ordering and give reasonably accurate results for the three lowest ionization potentials.