Ab initio potential energy surface and pressure broadening coefficients for the He-CH3F complex

Symmetry-adapted perturbation theory has been applied to compute the He-CH<sub>3</sub>F potential with the CH<sub>3</sub>F molecule assumed rigid. The potential has a global minimum of −48.9 cm<sup>−1</sup> at the center of mass separation of 7.2 bohr with the helium atom lying along the C-F bond on the hydrogen’s side. The computed points were fitted to an analytic energy surface with a correct asymptotic behaviour. This potential has been used to compute the pressure broadening (PB) coefficients for the (<em>j</em>, <em>k</em>) = (0, 0) → (1, 0) and (1, 0) → (2, 0) rotational transitions of CH<sub>3</sub>F perturbed by helium for a wide range of temperatures. Close-coupling results are compared with the experimental data of Willey et al. [J. Chem. Phys. 97 (1992) 4723], Beaky et al. [J. Mol. Struct. 352/353 (1995) 245] and infinite order sudden results are compared with those of Grigoriev et al. [J. Mol. Struct. 186 (1997) 48] for the <em>ν</em><sub>6</sub> band of CH<sub>3</sub>F perturbed by helium at room temperature. To our knowledge, present work is the first attempt of making fully ab initio calculations of collisional cross-sections and pressure broadening coefficients for this simple symmetric top system at low and room temperature.     

Aluminum(III) complexes containing O,O chelating ligand

The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>OH (LH) revealed compounds L<sub>3</sub>Al ( 1 ) and L<sub>2</sub>AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe<sub>2</sub> ( 3 ), rather 2 together with Me<sub>3</sub>Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph<sub>3</sub>SnOH, giving LSnPh<sub>3</sub> ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, <sup>1</sup>H, <sup>13</sup>C and <sup>119</sup>Sn NMR spectroscopy and <sup>1</sup>H, <sup>119</sup>Sn HMBC experiments. The system 2 and B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd.     

Coloring mixed hypertrees

A mixed hypergraph is a triple (<em>V</em>,<em>C</em>,<em>D</em>) where <em>V</em> is its vertex set and <em>C</em> and <em>D</em> are families of subsets of <em>V</em>, called <em>C</em>-edges and <em>D</em>-edges, respectively. For a proper coloring, we require that each <em>C</em>-edge contains two vertices with the same color and each <em>D</em>-edge contains two vertices with different colors. The feasible set of a mixed hypergraph is the set of all <em>k</em>'s for which there exists a proper coloring using exactly <em>k</em> colors. A hypergraph is a hypertree if there exists a tree such that the edges of the hypergraph induce connected subgraphs of the tree.We prove that feasible sets of mixed hypertrees are gap-free, i.e., intervals of integers, and we show that this is not true for precolored mixed hypertrees. The problem to decide whether a mixed hypertree can be colored by <em>k</em> colors is NP-complete in general; we investigate complexity of various restrictions of this problem and we characterize their complexity in most of the cases.     

On two mean value properties and functional equations associated with them

Summary Motivated by different mean value properties, the functional equations<i>f(x) – f(y)/x–y=<img src="/content/j17t6586453x3684/xxlarge966.gif" alt="phgr" align="MIDDLE" BORDER="0">[<img src="/content/j17t6586453x3684/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">(x, y)]</i>, (i)<i>xf(y) – yf(x)/x–y=<img src="/content/j17t6586453x3684/xxlarge966.gif" alt="phgr" align="MIDDLE" BORDER="0">[<img src="/content/j17t6586453x3684/xxlarge950.gif" alt="zeta" align="MIDDLE" BORDER="0">(x, y)]</i> (ii) (<i>x <img src="/content/j17t6586453x3684/xxlarge8800.gif" alt="ne" align="MIDDLE" BORDER="0"> y</i>) are completely solved when<i><img src="/content/j17t6586453x3684/xxlarge950.gif" alt="zeta" align="MIDDLE" BORDER="0">, <img src="/content/j17t6586453x3684/xxlarge331.gif" alt="eng" align="MIDDLE" BORDER="0"></i> are arithmetic, geometric or harmonic means and<i>x, y</i> elements of proper real intervals. In view of a duality between (i) and (ii), three of the results are consequences of other three.The equation (ii) is also solved when<i><img src="/content/j17t6586453x3684/xxlarge950.gif" alt="zeta" align="MIDDLE" BORDER="0"></i> is a (strictly monotonic) quasiarithmetic mean while the real interval contains 0 and when<i><img src="/content/j17t6586453x3684/xxlarge950.gif" alt="zeta" align="MIDDLE" BORDER="0"></i> is the arithmetic mean while the domain is a field of characteristic different from 2 and 3. (A result similar to the latter has been proved previously for (i).)     

Softening during and after the hot deformation of the AISI 321 steel with respect to practical applications

The softening processes during and after the hot deformation (850–1180 <img src="/content/r58782554401p411/xxlarge8225.gif" alt="Dagger" align="MIDDLE" BORDER="0">C) in AISI 321 stainless steel were studied with respect to true strains<i><img src="/content/r58782554401p411/xxlarge949.gif" alt="epsi" align="BASELINE" BORDER="0"></i> <sub>D</sub> and true strain rates <img src="/content/r58782554401p411/10582_2005_Article_BF01605409_TeX2GIFIE1.gif" alt=" $$\dot \varepsilon _D $$ " align="middle" border="0"> . The analysis of deformation curves indicates the occurrence of dynamic recrystallization for values of Zener-Hollomon parameter<i>Z</i><img src="/content/r58782554401p411/xxlarge8776.gif" alt="ap" align="MIDDLE" BORDER="0">10<sup>15</sup> s<sup>–1</sup>. The retardation of static recrystallization by fine Ti(N, C) precipitates is documented by microstructure studies and by variations of annealing conditions.     

Observation and analysis ofE mesons in\bar p p annihilation at rest in H2 gas

Antiproton-proton annihilation at rest in a gaseous H<sub>2</sub> target at NTP into the final state π<sup>+</sup> π<sup>?</sup> <em>K</em> <sup>±</sup> π<sup>?</sup> (<em>K</em> <sup>0</sup>) with an undetected<em>K</em> <sup>0</sup> or<span class="a-plus-plus inline-equation id-i-e2"> <span class="a-plus-plus equation-source format-t-e-x"> \(\bar K^0 \) </span> </span> has been investigated. We observe the<em>E</em>(1420) resonance in the invariant mass spectrum (<em>K</em> <sup>0</sup>)<sub>miss</sub> <em>K</em> <sup>±</sup> π<sup>?</sup> with mass<em>M</em> <sub> <em>E</em> </sub>=1413±8 MeV/c<sup>2</sup> and width<em>Г</em> <sup> <em>E</em> </sup>=62 ± 16MeV/c<sup>2</sup> and find evidence for the production of the<em>f</em> <sub>1</sub>(1285). The absolute branching ratio of<span class="a-plus-plus inline-equation id-i-e3"> <span class="a-plus-plus equation-source format-t-e-x"> \(\bar p\) </span> </span> <em>p</em> → π<sup>+</sup> π<sup>?</sup> <em>E</em> <sup>0</sup>,<em>E</em> <sup>0</sup> →<em>K</em> <span class="a-plus-plus stack"> <sub>0</sub> <sup> <em>L</em> </sup> </span> <em>K</em> <sup>±</sup> <em>π</em> <sup>?</sup> at (61±6)%<em>P</em> wave annihilation is (3.0±0.9)·10<sup>?4</sup> of all annihilations. The observed suppression of the<em>E</em> production from<em>P</em> wave with respect to the<em>S</em> wave together with some simple selection rules suggest that the quantum numbers of the<em>E</em>(1420) are<em>J</em> <sup>pc</sup>=0<sup>?+</sup> and not I<sup>++</sup>.     

Photophysical properties of borondipyrromethene analogues in solution

The photophysical properties of seven new 8-(p-substituted)phenyl analogues of 4,4-difluoro-3,5-dimethyl-8-(aryl)-4-bora-3a,4a-diaza-s-indacene (derivatives of the well-known fluorophore BODIPY) in several solvents have been studied by means of absorption and steady-state and time-resolved fluorimetry. For each compound, the fluorescence quantum yield and lifetime are lower in solvents with higher polarity owing to an increase in the rate of nonradiative deactivation. Increasing the electron withdrawing strength of the p-substituent on the phenyl group in position 8 also leads to lower fluorescence quantum yields and lifetimes. When the p-substituent on the phenyl group in position 8 is a tertiary amine [8-(4-piperidinophenyl), 8-(4-N,N-dimethylaminophenyl), and 8-(4-morpholinophenyl)], the low quantum yields of these compounds in more polar solvents can be rationalized by the inversion of the energy levels of an apolar, highly fluorescent and a polar, nonfluorescent excited state, where charge transfer from the tertiary amine to the BODIPY unit occurs. These amine analogues can be protonated at low pH in aqueous solution. Fluorescence titrations yielded pK(a) values of their conjugate ammonium salts which are in agreement with the electron donating tendency of the amine group: piperidino (4.15) > dimethylamino (2.37) > morpholino (1.47), with the pK(a) values in parentheses. The rate constant of radiative deactivation (k(f)) is the same for all compounds in all solvents studied (k(f) = 1.4 x 10(8) s(-1)).     

Z/E-photoisomerizations of olefins with 4npi- or (4n + 2)pi-electron substituents: zigzag variations in olefin properties along the T(1) state energy surfaces

[Figure: see text]. A quantum chemical study has been performed to assess changes in aromaticity along the T1 state Z/E-isomerization pathways of annulenyl-substituted olefins. It is argued that the point on the T1 energy surface with highest substituent aromaticity corresponds to the minimum. According to Baird (J. Am. Chem. Soc. 1972, 94, 4941), aromaticity and antiaromaticity are interchanged when going from S0 to T1. Thus, olefins with S0 aromatic substituents (set A olefins) will be partially antiaromatic in T1 and vice versa for olefins with S0 antiaromatic substituents (set B olefins). Twist of the C=C bond to a structure with a perpendicular orientation of the 2p(C) orbitals (3p*) in T1 should lead to regaining substituent aromaticity in set A and loss of aromaticity in set B olefins. This hypothesis is verified through quantum chemical calculations of T1 energies, geometries (bond lengths and harmonic oscillator measure of aromaticity), spin densities, and nucleus independent chemical shifts whose differences along the T1 PES display zigzag dependencies on the number of -electrons in the annulenyl substituent of the olefin. Aromaticity changes are reflected in the profiles of the T1 potential energy surfaces (T1 PESs) for Z/E-isomerizations because olefins in set A have minima at 3p* whereas those in set B have maxima at such structures. The proper combination (fusion) of the substituents of set A and B olefins could allow for design of novel optical switch compounds that isomerize adiabatically with high isomerization quantum yields.