The kinetics of the “a” and “b” band emissions arising from the 1Σ ← 3Ou and 1Σ ← 3lu transitions of the diatomic mercury molecule at λmax ~ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N2, C2H6, C3H8, and N2O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg2(3lu) + N2 → Hg2(3Ou) + N2 and Hg2(3Ou) + RH → Hg2(1Σ) + RH, where RH = C2H6 or C3H8. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(3P0) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry. 相似文献
Summary: An oil‐in‐water high internal phase emulsion consisting of acrylic acid, water, and a crosslinker (N,N′‐methylene bisacrylamide) as the water phase, and toluene as the oil phase was successfully stabilised to sustain thermal initiation of radical polymerisation resulting in porous open‐cellular monolithic material. The type of initiator used influenced the average pore size ranging from approx. 708 nm to approx. 1 087 nm, as determined by mercury porosimetry.
Schematic of the preparation of an oil‐in‐water‐type polyHIPE (high internal phase emulsion). 相似文献
The internal functionalization of the Keplerate‐type capsule Mo132 has been carried out by ligand exchange leading to the formation of glutarate and succinate containing species isolated as ammonium or dimethylammonium salts. Solution NMR analysis is consistent with asymmetric inner dicarboxylate ions containing one carboxylato group grafted onto the inner side of the spheroidal inorganic shell while the second hangs toward the center of the cavity. Such a disposition has been confirmed by the single‐crystal X‐ray diffraction analysis of the glutarate containing {Mo132} species. A detailed NMR solution study of the ligand‐exchange process allowed determining the binding constant KL of acetate (AcO?), succinate (HSucc?) or glutarate (HGlu?) ligands at the 30 inner coordinating sites, which vary such as K<K<K‐supported by the associated thermodynamic parameters ΔrS* and ΔrH*. Such a variation is mainly explained by a positive entropic gain attenuated by unfavorable steric effect. Furthermore, these results are completed by 1H DOSY and 1H EXSY NMR experiments which are in agreement with bulky guests firmly trapped within the cavity. At last, variable temperature 1H NMR study below 290 K revealed a striking line broadening occurring abruptly within a 5 K range. Such an effect appears closely related to the presence of the ammonium cations suspected to be present within the cavity and then has been interpreted as an inner‐phase transition leading to a frozen state. 相似文献
The critical strain εc for crazing of polystyrene in each of a variety of organic liquids has been measured along with the degree of swelling of the polymer by the liquid and the attendant reduction in the glass transition temperature Tg of the polymer. The critical strain for the crazing in air and the Tg of each of a set of specimens molded from mixtures of o-dichlorobenzene and polystyrene have also been determined. Correlations of εc with Tg in the two cases are identical within experimental error for the first 40°C of Tg reduction; these results imply (1) that organic liquids do not exercise a significant surface energy role in solvent crazing and (2) that their only roles are associated with flow processes. Correlation of solvent crazing εc with solubility parameter of the crazing fluid is very poor for several reasons that are discussed. 相似文献
The scheme of ‘through-space’ and ‘through-bond’ interaction of (semi)localized orbitals, originally proposed by Hoffmann, is reexamined in terms of SCF many-electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off-diagonal matrix elements of the Hartree-Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalized Hartree-Fock matrices referring to ‘precanonical orbitals’. The procedure outlined is applied to three practical examples using the semiempirical many-electron treatments SPINDO, MINDO/2 and CNDO/2:
a A reassessment of ‘through-space’ and ‘through-bond’ interaction in norbornadiene indicates, that the latter type of interaction is also of importance for the orbital based mainly on the antisymmetric combination of the localized x-orbitals. The differences in the predictions derived from the three models are critically examined.
b The competition between ‘through-space’ and ‘through-bond’ interaction in the series of bicyclic dienes from norbornadiene to bicyclo[4.2.2]-dcca-7,9-diene and in cyclohexa-1,4-diene, i. e. their dependence on the dihedral angle UI is reexamined. It is found that the rationalization for the orbital crossing near ω = 130° deduccd from PE. spectroscopic data can not be as simple as originally suggested and that the relay’ orbitals responsible for ‘through-bond interaction affecting both the symmetric and the antisymmetric combination of the π-orbitals extend over the whole CC-σ-system of the six membered ring.
c ‘Through-bond’ interaction of the two lone pair orbitals in 1,4-diazabicyclo[2.2.2]octane is found to be large for their symmetric and the antisymmetric linear combination.
The analysis quoted, draws attention to some of the dangers involved in using semiempirical treatments for the interpretation of PE. data in terms of Koopmans′ theorem, without due caution. 相似文献
As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron‐rich guests and detail the influence of encapsulation on the charge‐transfer interactions between guests. For the mono‐bipyridinium guest (methylviologen, MV 2+), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge‐transfer interactions between methylviologen and dihydroxynaphthalene ( HN ) by mainly forming the 1:2:1 packed “sandwich” complex (CB[10] ? 2 MV 2+ ?HN ). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to “U” shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane‐blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X‐ray crystal structure. Finally, a supramolecular “Russian doll” was built up by threading a guest through the cavities of both blue box and CB[10]. 相似文献
Kinetic and spectrophotometric measurements made during the Fe3+ ion catalyzed decomposition of H2O2 have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k3/KM = 4.94 M?1 min?1, k4 = 193 M?1 min?1, εI/KM = 52.3 M?2 cm?1, εII = 25.7 M?1 cm?1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O2 evolved in the reaction using [H2O2] ~ 10?2 M has been calculated and found to be nearly stoichiometric. O2 evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O2 and the “free radical mechanism” predicting exactly stoichiometricamounts of O2. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H2O2 both with Fe2+ and Fe3+ ions, as well as other reactions assumed to proceed via free radicals. 相似文献