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91.
Lesar A Kovacic S Hodoscek M Mühlhäuser M Peyerimhoff SD 《The journal of physical chemistry. A》2005,109(45):10357-10362
A theoretical study of the low-lying singlet and triplet states of ClONO is presented. Calculations of excitation energies and oscillator strengths are reported using multireference configuration interaction, MRD-CI, methods with the cc-pVDZ + sp basis set. The calculations predict the dominant transition, 4(1)A' <-- 1(1)A', at 5.70 eV. The transition 2(1)A' <-- 1(1)A', at 4.44 eV, with much lower intensity nicely matches the experimental absorption maximum observed around 290 nm (4.27 eV). The potential energy curves for both states are found to be highly repulsive along the Cl-O coordinate implying that direct and fast dissociation to the Cl + NO2 products will occur. Photodissociation along the N-O coordinate is less likely because of barriers on the order of 0.3 eV for low-lying excited states. A comparison between the calculated electronic energies related to the two dominant excited states of ClONO and BrONO indicates that the transitions lie about 0.6 eV higher if bromine is replaced by chlorine. The stratospheric chemistry implications of ClONO and BrONO are discussed. 相似文献
92.
E. J. Knust R. Wortmann H. -J. Machulla 《Journal of Radioanalytical and Nuclear Chemistry》1989,129(1):85-91
Using a distillation method for the separation of18F-fluoride from aqueous18F-solutions obtained after cyclotron irradiation of a water target by means of the16O(3He, p)18F reaction, the radiohalogen could be generated as a highly reactive species for nucleophilic substitution reactions. Thus, with the starting compounds 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl--D-mannopyranose and 1,2:5,6-di-O-isopropylidene-3-O-trifluoromethanesulfonyl--D-allofuranose18F-2-deoxy-2-fluoro-D-glucose (2-18FDG) and18F-3-deoxy-3-fluoro-D-glucose (3-18FDG) could be synthesized with radiochemical yields of 71.6% and 85.9%, respectively. Including purification by HPLC, the total preparation time was 70 min, yielding the glucose derivatives in a no-carrier-added state. Specific activities coold be calculated to be greater than 103 Ci/mmol. 相似文献
93.
Traces of fluoride can be separated from aqueous solution by extraction with (C2H5)3SiCl in m-xylene or with (C6H6)4SbOH in CH2Cl2. Furthermore, several coprecipitation reactions were tested; adsorption on hydroxyl apatite is most suitable.Determination of 0.05 μg F?/ml can be performed by gas chromatography of (C2H5)3SiF in m-xylene using flame ionisation detectors; but variable blanks of 0.5–1.5 μg F? normally prevent the determination of less than ca. 3 μg F?. 相似文献
94.
Nováková S Van Dyck S Van Schepdael A Hoogmartens J Glatz Z 《Journal of chromatography. A》2004,1032(1-2):173-184
This review describes the existing developments in the use of the capillary electrophoretic microanalytical technique for the in-line study of enzyme reaction, electrophoretically mediated microanalysis (EMMA). The article is divided into a number of parts. After an introduction, the different modes, basic principle, procedure, and some mathematical treatments of EMMA methodology are discussed and illustrated. The applications of EMMA for enzyme assay and for non-enzymatic determination are summarized into two tables. In addition to classical capillary electrophoresis (CE) instrument EMMA, special emphasis is given to a relatively new technique: EMMA on CE microchip. Finally, conclusions are drawn. 相似文献
95.
Ab initio SCF calculations are reported for the potential surfaces of the HCO+ and COH+ molecular ions in both ground and low-lying excited states. An analysis of the bonding characteristics of the two systems is undertaken, from which it is noted that the 5σ and 1π orbital energy levels in HCO+ are inverted relative to the order found in both COH+ and also in CO itself. This fact leads to a situation in which the (1π, 2π) excited states of HCO+ as well as the ground state are more stable than their COH+ counterparts, whereas the opposite relationship is observed for (5σ, 2π) species. In addition it is pointed out that those states which populate the 7a' in-plane component of the 2π MO in either molecule-ion are characterized both by bent equilibrium structures and also by dissociation into CO+ + H, whereas all other low-lying species, including the ground state, prefer linear structures which dissociate via a CO + H+ channel. 相似文献
96.
Large-scale ab initio multi-reference configuration interaction (MRD-CI) calculations are carried out to determine the vertical electronic spectrum of HC9H. The calculated energy for the first dipole-allowed 3Σu−←X 3Σg− transition of 2.38 eV is in reasonable agreement with recent measurements of 582 nm (2.13 eV) in neon matrix. The oscillator strength is computed with f=0.007. In addition a second very strong (f=4.7) 3Σu−←X 3Σg− transition is predicted by the calculations to be located near 6 eV. 相似文献
97.
Summary A method for representing inactive groups, i.e. spectator groups, in a molecular system by an effective potential is presented. The matrix elements for the spectator's short-range Hartree-Fock potential is stored in an intermediate AO basis, from which it can be transferred into the user basis for the active part of the molecular system. The longer-range of the potential is transferred via a (distributed) multipole expansion. The method is illustrated for the NH3·X (X=NH3, H2O, HF) complexes: binding energies could be reproduced to within 5% by employing the effective NH3 potential (whereby the lone pair was included in the active system), the entire NH3·HF potential curve with a depth of 50 kJ/mol is reproduced within 2 kJ/mol if various intermediate basis sets are chosen. Technical details are discussed; the effective potential can directly be introduced in CI calculations. 相似文献
98.
99.
100.
Weigelt S Busse C Nielsen M Gothelf KV Laegsgaard E Besenbacher F Linderoth TR 《The journal of physical chemistry. B》2007,111(39):11342-11345
The adsorption structures formed from a class of oligophenylene-ethynylenes on Au(111) under ultrahigh vacuum conditions is compared based on high-resolution scanning tunneling microscopy (STM) measurements. The molecules consist of three or four benzene rings connected by ethynylene spokes and are all functionalized identically with an aldehyde, a hydroxyl, and a bulky tert-butyl group. Compounds with the conjugated spokes placed in the para, meta, and threefold configurations were previously found to exclusively form molecular layers with flat-lying adsorption geometries. In contrast, the associated compound with spokes in the ortho configuration surprisingly differs in its adsorption by forming only structures with an upright adsorption orientation. The packing density for the structures formed by the compound with the ortho configuration is less dense than that in conventional self-assembled monolayers while still keeping the conducting backbone in an upright orientation. These structures are thus interesting from the perspective of performing single-molecule conduction measurements on the oligophenylene-ethynylene backbones. 相似文献