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1.
The 12B1(X2B1), 12B2, 12A1, 12A2, 22B2, and 22A1 states of the ion were studied using CASPT2 and CASSCF methods. Calculations suggest that one should consider the 32A′ state instead of 22B2. The CASPT2 T0 calculations predict the energy ordering of 12B1(X2B1), 12B2, 12A1, 12A2, 32A′, and 22A1, which is in line with the experimental results by Pradeep and Shirley. The CASPT2 T0 values for the 12B2, 12A2, 32A′, and 22A1 states are close to the experimental values. The F-loss and H-loss dissociation processes were studied at the CASPT2//CASSCF level. The energy levels of low-lying states of are compared. 相似文献
2.
Low temperature absorption spectra of benzene films were observed in the 1B1u ← 1A1g transition region. The origins of the two progressions of the totally symmetric vibration v2(a1g) are assigned to the crystal-field-induced 0—0 transition and to the false origin 0 + v1g(e2g). 相似文献
3.
The stable thromboxane A2 analog (±)-dimethanothromboxane A2 1 was synthesized from bicyclo[3.1.1]heptane 2 via the tricyclic compound 4. 相似文献
4.
Elena Buixaderas Elena Maria Anghel Simona Petrescu 《Journal of solid state chemistry》2010,183(9):2227-2235
Composites in the TiB2-Na2O·B2O3·Al2O3 systems, TiB2-MBA (MB stands for sodium metaborate and A is Al2O3), were prepared by self-propagating high-temperature synthesis (SHS), in simultaneous mode. Selection of these compositions was ruled by the interesting properties of both TiB2 and double borates of alkali metal and aluminum. The structure of the obtained materials was evaluated by micro-Raman spectroscopy, from room temperature up to 600 °C, and X-ray photoelectron spectroscopy (XPS). Formation of the TiB2 and TiO2−xBx phases along with TiO2 as rutile were identified as titanium speciation in the grain phase embedded in a sodium aluminum borate matrix. Integration of the Raman spectra of the grain phases revealed a TiB2 content of 16.99% and 23.32% for the two composite investigated 2TiB2·2MBA and 3TiB2·5MBA. A constrained-width model for the spectral deconvolution of the high-frequency Raman band was forwarded to calculate the proportion of tetrahedral boron atoms (7.424%) in the blank borate matrix Na2B2O4·Al2O3 in solid phase. 相似文献
5.
The total synthesis of (±)-11a-methano- 9,11-thiathromboxane A2(1), the sulfur analog of thromboxane A2 is described 相似文献
6.
7.
(+)-11a-methano-9,11-thiathiromboxane A2(1) was synthesized from prostaglandin A2 and prostaglandin E2. 相似文献
8.
MCD measurements have been used to estimate the ground- and excited-state magnetic moments and zero-field splittings for the 4A2 → 2E(2D) transition in Cs3CoCl5. 相似文献
9.
Stereoselective syntheses of the naturally occurring glycosidase inhibitors hyacinthacines A2 and A3 are reported. In the case of hyacinthacine A2, the pyrrolizidine system was created from an acyclic precursor via a double cyclization procedure with a one-pot formation of two C-N bonds. In the case of hyacinthacine A3, the two C-N bonds were created in separate steps. In addition, the non-natural epimer at C-5 of hyacinthacine A3 was obtained. 相似文献
10.
Polarised IR and Raman spectra for KH2PO3 single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO3 groups.
The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions. 相似文献
11.
The total synthesis of (±)-dithiathromboxane A2 sodium salt 1 was accomplished in 26 steps from methyl 4,4-dimethoxyactoacetate. 相似文献
12.
The jet-cooled p-cyanobenzyl radical has been generated from p-tolunitrile and vibronically excited with a carrier gas, He, using a pinhole-type nozzle in a corona excited supersonic expansion. The vibronic emission spectrum of the p-cyanobenzyl radical in the transition of D1(2 2B2)→D0(1 2B2) has been recorded with a long-path monochromator in the visible region. The spectrum was analyzed to obtain the vibrational mode frequencies of the p-cyanobenzyl radical in the ground electronic state with the aid of an ab initio calculation as well as those of p-tolunitrile. 相似文献
13.
Giannoula Theodorakopoulos Ioannis D. Petsalakis Cleanthes A. Nicolaides Robert J. Buenker 《Chemical physics》1985,100(3)
Oscillator strengths for transitions between the
1A1 ground state of water and its
1A1 and
1A1 excited states are computed employing two different theoretical approaches. In one series of calculations a common orthonormal one-electron basis is employed for all of the above states, while in the other type of treatment two different, mutually non-orthogonal, sets are used; the multireference single- and double-excitation (MRD CI) method is employed in each case, with configuration selection, to generate the various electronic wavefunctions. It is found that the use of ground-state SCF MOs leads to poor convergence in the wavefunctions of the (Rydberg-type)
1A1 and
1A1 excited states and consequently also for the corresponding
---
and
---
f-values; this behavior is seen to be closely related to the near degeneracy of the two excited states, each of which is a mixture of the 3a1 → 3sa1 and 1b1 → 3pb1 configurations. Analogous computations with the
1B11b1 → 3sa1 MOs show much better convergence properties, and the resulting f-values compare well with what is obtained when state-specific orbital sets are employed separately for ground and excited states and non-orthonormal techniques are applied to compute the desired transition moments. These results tend to confirm previous findings which indicate conceptual and computational advantages for the calculation of excited-state wavefunctions and properties within the context of a state-specific theory. They also show that although the goal of eliminating the dependence of MRD CI calculations on the choice of MO basis is very nearly approached for energy quantities, it is less satisfactorily achieved for other properties, especially when the existence of nearly degenerate electronic states is a critical factor. 相似文献
14.
Monir Amin 《Fresenius' Journal of Analytical Chemistry》1987,329(5):600-602
Summary A direct, quantitative, thin-layer chromatographic (TLC) method is described for the separation and determination of a PGE2-descendant (compound I = PGE2-desc.), a PGA2-descendant (compound II = PGA2-desc.) and a PGB2-descendant (compound III = PGB2-desc.) as pure substances and in pharmaceutical preparations. The extraction of the active ingredients is performed in a fully automated apparatus within 5 min. Using TLC compound I (UV-inactive substance) must be converted into compound III so that it can be measured at -max. 280 nm. Compound II can be measured both directly at -max. 224 nm and after conversion into compound III [1]. The conversion of PGE2-desc. and PGA2-desc. into PGB2-desc. was achieved after spraying the separated PG-spots on the TL-plates with KOH solution and heated. The TLC development was carried out on silica gel 60 F254 and measurement was direct on the plates by chromatogram spectrodensitometry using the reflection method. The method is also suitable for stability studies and has also proved useful in the analysis of the prostaglandin-derivatives in various pharmaceutical preparations.
Quantitative dünnschicht-chromatographische Bestimmung einiger Prostaglandinderivate der Untergruppen E2, A2 und B2相似文献
15.
Jean-Paul Pinan-Lucarre 《Chemical physics letters》1983,98(2):195-198
The isotropic and anisotropic Raman spectra of a pure liquid and a dilute isotopic solution are compared. In the light of the theories of Tarjus and Bratos, the experimental results allow a quantitative separation of the self and distinct pair vibrational contributions to the isotropic spectrum of the pure substance. It is found that the anisotropic spectrum depends only on the self vibrational term. 相似文献
16.
A novel optical chemical sensor based on the dynamic liquid drops combined with flow injection-solid phase has been developed for continuous and sequential determinations of the mixture of Vitamin B1, Vitamin B2 and Vitamin B6. The design and characteristics of the sensor system are described. The dynamically growing and falling drops serve as windowless optical cells. The adsorption, desorption and quantitative determinations of VB1, VB2 and VB6 were carried out based on selective adsorption of Sephadex CMC-25 and different fluorescence characteristics of VB2, VB6 in the basic solutions. The optimum analytical conditions for compound Vitamin B assay have been established. Under these conditions, linear calibration curves were obtained over the range of 0.01-8.00, 0.01-10.00 and 0.01-3.00 μg/ml for VB1, VB2 and VB6 with the limits of determination of 0.008, 0.005 and 0.006 μg/ml, respectively. This method has been applied in the determination of synthetic mixture of VB1, VB2, VB6 and Vitamin B compound tablets with satisfactory results. The technique, which has been described, provides a simple, effective and sensitive method to assay the biological samples. 相似文献
17.
We have found for the first time a ferroelastic transition in many molybdates and tungstates with the Sc2(MoO4)3-type structure. Below the transition these phases are monoclinic (), and above the transition they are orthorhombic (Pnca). Observed transition temperatures are: Al2(MoO4)3, 200°C; Al2(WO4)3, ?6°C; Cr2(MoO4)3, 385°C; Fe2(MoO4)3, 499°C; In2(MoO4)3, 335°C; In2(WO4)3, 252°C; and Sc2(MoO4)3, 9°C. 相似文献
18.
The benzene 1B2u → 1A1g emission spectrum is observed in a flowing argon afterglow by a low power microwave discharge. No emission of dissociation products was found in 2000–7000 Å region. 相似文献
19.
Mitsuyo Horikawa Toshihiro Hashimoto Shigeru Takaoka Hiroto Kaku Kentaro Yamaguchi Masaki Kawase Masao Sato 《Tetrahedron》2006,62(38):9072-9076
Two novel red pigments, uroleuconaphins A1 (1) and B1 (2) were isolated from the aphid Uroleucon nigrotuberculatum (Olive). The structures and the absolute configurations of 1 and 2 were determined by single-crystal X-ray analysis of their derivatives. These structures were constituted as dimeric compounds of two molecules of quinone A (3), which were linked via a dihydrofuran ring system. 相似文献
20.
P. Biggs G. Hancock M. R. Heal D. J. McGarvey A. D. Parr 《Chemical physics letters》1991,180(6):533-540
Absolute rate constants for the removal of CH2 (ã 1A1) by Ar, NO and H2 have been measured over the temperature range 295–431 K using laser flash kinetic absorption spectroscopy. For NO and H2, no marked temperature dependence is observed. For Ar, the rate constants increase by some 50% over this range and the results are discussed in terms of a theoretical model which relates the removal rate constants to the fractional population of CH2 (ã 1A1) in states perturbed by nearby triplet levels. 相似文献