共查询到20条相似文献,搜索用时 31 毫秒
1.
Structural and electronic properties of semiconductor binary microclusters cations have been investigated using the B3LYP-DFT method in the ranges of n=1, 2 and m=1–7. Full structural optimization, adiabatic ionization potentials calculation and frequency analysis are performed with the basis of 6-311+G(d). The charged-induced structural changes in these cations have been discussed. The strong As–As bond is also favored over Al–As bonds in the cations in comparison with corresponding neutral cluster. With Asm forming the base, adding Al atom(s) in different positions would find the stable structures of cations quickly and correctly. , , and are predicted to be species with high stabilities and possible to be produced experimentally. 相似文献
2.
Is Cd2 truly a van der Waals molecule? Analysis of rotational profiles recorded at the , transitions
Rotational profiles of the 228Cd2 isotopomer recorded in the (υ′, υ″) = (26, 0), (27, 0), (42, 0), (45, 0), (46, 0), (48, 0) vibrational bands of the transition were analysed. As a result, the , , , , and excited- as well as the ground-state rotational constants of the (114Cd)2 were determined. The analysis allowed determining the absolute values for the and excited- and ground-state bond lengths, respectively. The obtained result – the – distinctly shorter than that obtained with assumption of pure ground-state van der Waals bonding, supports a theoretical prediction of a covalent admixture to the bonding. Analysis of the partially-resolved rotational profile recorded in the (υ′, υ″) = (38, 0) band of the same isotopomer recorded at the transition allowed estimating the rotational constant in the B1u state. 相似文献
3.
F. Kariya K. Ebina K. Hasegawa K. Koshimizu B. Wuritunasitu K. Hondou S. Ebisu S. Nagata 《Journal of solid state chemistry》2009,182(8):2018-2023
The spinel sulphide CuCr2S4 is a metallic ferromagnet with a Curie temperature , while CuHf2S4 has no magnetic anomaly. Magnetic properties of the quaternary spinel-type Cu(Cr1-xHfx)2S4 system have been studied. With increasing x the ferromagnetic properties are weakened gradually from a predominant ferromagnetic, a spin-glass, finally to a simple paramagnetic behavior. For the composition of x0.50, a re-entrant spin-glass phase could emerge, even though the Curie temperature is ill-defined as a ferromagnetic phase boundary. Specimens with x≥0.90 remain paramagnetic down to 4.2 K. A spin crossover phenomenon is found around 160 K in the specimens of x=0.50–0.70. A step-like anomaly is manifestly detected in the magnetization, which corresponds with the change of the spin state. This crossover indicates that the spin state converts from high temperature S=2 into low temperature states. In the ordered states in , the magnetic moment originates from only Cr3+ ions. 相似文献
4.
Susanne Salzmann Jrg Tatchen Christel M. Marian 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):221-231
The ground and low-lying excited electronic states of isoalloxazine, 10-methylisoallox-azine and lumiflavin, three flavin-related compounds, were investigated by means of quantum chemical methods. Minimum structures were determined employing (time-dependent) Kohn–Sham density functional theory. Spectral properties were computed utilizing a combined density functional and multi-reference configuration interaction (DFT/MRCI) method. Solvent effects were mimicked by a conductor like screening model and micro-hydration with four explicit water molecules. At selected points along a linearly interpolated path connecting the Franck–Condon region and the S1minimum, spin–orbit interaction was computed employing a nonempirical mean-field Hamiltonian. For isoalloxazine, intersystem crossing (ISC) rate constants were computed, taking both direct and vibronic spin–orbit coupling into account.On the basis of these calculations we suggest the following photo relaxation model. In the vacuum, efficient ISC takes place between the primarily excited state (S1) and the lowest state (T2). The energetic proximity of the state (S2) enhances the nonradiative relaxation of S1 by internal conversion (IC). In aqueous solution these ISC and IC channels are energetically not accessible due to the blue shift of the states. The high triplet quantum yield observed in experiment [J.T.M. Kennis, S. Crosson, M. Gauden, I.H.M. van Stokkum, K. Moffat, R. van Grondelle, Biochemistry 42 (2003) 3385–3392] is explained by the intersection between the state (S1) potential energy hypersurface (PEH) and the second (T2) PEH along the relaxation pathway and the strong enhancement of their spin–orbit coupling by vibronic interactions. The calculated ISC rate for this channel is in good agreement with experimental results. According to our model, lack of an efficient IC channel leads to an increased fluorescence quantum yield in aqueous solution. 相似文献
5.
Ramon Barnadas-Rodríguez Joan Estelrich 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):262-267
Pyranine is a pH-sensitive fluorescent probe useful in the pH range of 4.5–8, and it has been extensively employed to determine pH inside cells, membranes and membrane models. The fluorescent properties of pyranine are a consequence of the excited states ROH* and RO−*. The prototropic equilibrium of these excited species has a much lower than that of the ground state. In this paper we determined the (1.42 ± 0.06) and the relative quantum yield of pyranine in the pH range of 1–8 by analyzing the component peaks of the steady-state of the dye's emission spectrum. As pyranine is very sensitive to the medium we studied the influence of salts formed by mono-, di-, and trivalent ions on the apparent . In all cases, the presence of salts reduced the apparent to varying degrees depending on the valence of the cations. The strategy used to obtain this information was a dual emission ratiometric method at 441 and 511 nm after excitation at 350 nm. The results obtained demonstrate that pyranine is suitable to determine the pH of aqueous solutions in the range of 1–3.5. 相似文献
6.
Michiko Atsumi Leticia Gonzlez Chantal Daniel 《Journal of photochemistry and photobiology. A, Chemistry》2007,190(2-3):310-320
The absorption spectroscopy of [Ru(phen)2dppz]2+ and [Ru(tap)2dppz]2+ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen)2dppz]2+ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT () absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap)2dppz]2+ between 522 nm and 400 nm is the presence of various excited states such as MLCT (), ligand-to-ligand-charge-transfer LLCT () or intra-ligand IL () states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H2O, CH3CN) the absorption spectrum of [Ru(tap)2dppz]2+ is dominated by a strong absorption at 388 nm (CH3CN) or 390 nm (H2O) assigned to a 1IL () corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the 1IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA. 相似文献
7.
8.
A systemic density functional theory study of the tin-doped carbon clusters has been carried out using B3LYP method with TZP+ basis set. For each species, the electronic states, relative energies and geometries of various isomers are reported. Except for smaller SnC2 and the largest , the Sn-terminated linear or quasi-linear isomer is the most stable structure for clusters. The electronic ground state is alternate between 3Σ (for n-odd member) and 1Σ (for the n-even member) for linear SnCn and invariably 2Π for linear and , except for SnC/SnC+/SnC−,, and . The incremental binding energy diagrams show that strong even–odd alternations in the cluster stability exist for both neutral SnCn and anionic , with their n-even members being much more stable than the corresponding odd n − 1 and n + 1 ones, while for cationic , the alternation effect is less pronounced. These parity effects also reflect in the ionization potential and electron affinity curves. By comparing with the fragmentation energies accompanying various channels, the most favorable dissociation channel for each kind of the clusters are given. All these results are very similar to those obtained previously for the clusters. 相似文献
9.
Guoliang Li Xiaohong Li Chaoyang Wang Guozheng Ma 《Journal of Molecular Structure》2009,910(1-3):50-55
The lithium-doped carbon clusters LiCn, , and (n = 1–10) have been investigated systemically with density functional theory (DFT) method at the B3LYP/6-311+G* level. According to the total energies of different kinds of isomers, the LiCn, , and (n = 1–10) clusters have Li-terminated linear ground states structures, except for LiC2, LiC3, , and (n = 4–6). The incremental binding energies are evaluated to elucidate the stabilities of the clusters with different numbers of carbon atoms for neutral molecules, cations, and anions, respectively. Clear even–odd alternation effects are observed for the stability of the cationic clusters and anionic clusters, while for neutral LiCn clusters the alternation effect is less pronounced. Similarly, the ionization potentials and electron affinities of LiCn also express an obvious parity alternation. In addition, the most favorable dissociation channels are acquired according to the fragmentation energies accompanying various pathways. 相似文献
10.
Ping Zuo Adita Sutresno Chunyong Li Yasushi Koyama Hiroyoshi Nagae 《Chemical physics letters》2007,440(4-6):360-366
In all-trans-neurosporene, whose level is lower than the level by one vibrational quantum, the following two steps of vibrational relaxation from the mixed vibronic states were identified, in the order, stimulated emission stimulated emission transient absorption. The stimulated emission patterns were simulated by the use of Franck–Condon factors in the transitions from the pair of mixed vibronic levels down to the ground vibronic levels. The vibronic levels of the mixed and state were characterized theoretically based on the diabatic approximation. 相似文献
11.
Rate coefficients (k) of CH2OH, , and radical addition to maleic and fumaric acids were investigated between pH 1 and 8. Strong pH dependences observed were attributed to changes in protonation states of acids: H2X, HX− and X2−. k of CH2OH, , addition to fumaric acid decreased in the order kH2F>kHF->kF2- in agreement with the nucleophilic character of reaction. The electrophilic radical showed opposite tendency. With maleic acid the monoanion had the highest reactivity towards nucleophilic and the lowest one towards electrophilic radicals. This is attributed to a prevalence of steric over polar effects for HM−. 相似文献
12.
The electronic structure of the ground state of has been investigated using relativistically-corrected CCSD(T) in conjunction with ANO-RCC (Mg) and aug-cc-pVQZ (H) basis sets. The molecular potential energy surface possessed minima corresponding to both 1A1 and equilibrium structures (with a 1Σ+ transition state). The 1A1 structure possessed Re and θe values of 2.0297 Å and of 22.09°, respectively. The higher-energy structure exhibited an Re value of 2.1658 Å. Property surfaces were constructed to calculate rovibrational energies and spectral line intensities for the ground states of , (1A′) MgHD2+ and . For the vibration ground state of , the vibration-averaged Re and θe values were calculated to be 2.0209 Å and 22.53°, respectively. The A, B and C rotational constants were calculated to be 58.0, 2.21 and 2.11 cm−1, respectively. 相似文献
13.
Renzhong Li Xiaowei Zhang Haiyan Zheng Jun Liang Zhifeng Cui 《Journal of Molecular Structure》2008,860(1-3):106-110
Geometry optimization and harmonic vibrational frequency calculations were performed on the and states of HOO and state of HOO−. The electron affinity and the term energy () of HOO were calculated at various theory levels. Franck–Condon analyses and spectral simulations were carried out on the and photodetachment processes. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in excellent agreement with the observed spectra. In addition, the equilibrium geometrical parameters of the state of HOO− and state of HOO were obtained in the spectral simulations. 相似文献
14.
Ionic fragmentation following the inner-shell photoexcitation of [(CH3)2CO]Arn heteroclusters was investigated in the Ar L23- and O K-edge regions. A partial ion yield (PIY) measurement revealed that and various acetone fragments (, , , , and CHmCO+) were produced following the Ar L23-shell excitation. In the O K-edge region, the PIY of O+ exhibited a sharp resonance peak at the O 1s → π*(CO) resonance excitation. The selective O+ formation was interpreted as the suppression of statistical fragmentation, which was dominant in isolated acetone, owing to the dissipation of excess energy into Ar clusters. 相似文献
15.
Ryuji Itakura Takatsugu Tanaka Mikinori Kuwata Hideaki Suzuki Kaoru Yamanouchi 《Chemical physics letters》2008,462(1-3):27-30
Photodecomposition processes of 2-, 3-, and 4-methylaniline cations induced by a moderately intense (1011 W/cm2) visible nanosecond laser field and an intense (1015 W/cm2) UV femtosecond laser field have been investigated using a tandem mass spectrometer. Highly unsaturated fragment cations such as and are dominantly produced by the nanosecond laser, while less unsaturated smaller fragment cations such as , and are produced mainly by the femtosecond laser. Ab initio calculations have also been performed to estimate the stable geometrical structures of and and those of possible intermediate ring compounds for discussing the photodecomposition pathways in intense laser fields. 相似文献
16.
J. Troncoso C.A. Cerdeiria P. Losada-Prez E. Carballo L. Romaní 《Fluid Phase Equilibria》2009,280(1-2):144-150
We present a comprehensive study of the behaviour of excess second-order derivatives of binary mixtures near the liquid–liquid critical point. Specifically, excess (isobaric and isochoric) molar heat capacities ( and ), excess (isothermal and isentropic) compressibilities ( and ), and excess isobaric thermal expansivities () have been determined over the whole composition (x) range at atmospheric pressure and in the homogeneous region within (293.15–323.15) K. Results are consistent with the predictions of the current theory of critical phenomena. Remarkably, anomalous and curves in the critical region are observed. Such anomalies, which are reported here for the first time, are of significant size for and very mild in the case of , thereby indicating that volumetric effects at near-liquid–liquid criticality are, as expected, very small. 相似文献
17.
A new mixed-valent manganese phosphate, , has been synthesized using hydrothermal method. Its monoclinic C2/c structure (a=12.5506(16) Å, b=10.4816(18) Å, c=13.6723(10) Å, β=103.758(11)°) forms a 3D framework of MnO6 octahedra, MnO5 trigonal bipyramids, PO4 and PO3OH tetrahedra. The main structural feature of this phosphate deals with its [Mn4O16]∞ chains running along , which are interconnected through PO4 and PO3OH tetrahedra, forming intersecting tunnels running along [110], and [001]. The geometry of the [Mn4O16]∞ chains and the charge ordering of manganese in the latter are unique: they consist of trimeric units of divalent manganese “” alternating with single trivalent MnIIIO6 octahedra along . In each “” unit one central MnIIO6 octahedron shares two opposite edges with two MnIIO5 trigonal bipyramids. Along , one Mn(II) octahedron alternates with one Mn(III) octahedron by sharing one corner. The relationships between the structure of this unique charge ordered phosphate and other manganese phosphates are discussed. 相似文献
18.
Martin Breitenfeldt Sudarshan Baruah Klaus Blaum Alexander Herlert Martin Kretzschmar Franklin Martinez Gerrit Marx Lutz Schweikhard Noelle Walsh 《International journal of mass spectrometry》2008,275(1-3):34-44
The application of an additional azimuthal quadrupolar electrostatic field to a Penning trap leads to a field configuration referred to as an elliptical Penning trap. The resulting changes of the radial ion motions have been investigated experimentally and by use of simulations. The eigenfrequencies, i.e., the magnetron frequency and the reduced cyclotron frequency , are found to be shifted with respect to those of the standard Penning trap ω−, ω+, respectively. As the shift of the magnetron frequency is larger than that of the reduced cyclotron frequency their sum is also a function of the ellipticity and no longer equal to the cyclotron frequency in the absence of an electric trapping field ωc=qB/m. The frequency shifts were investigated for argon and fullerene ions. The experimental studies were performed by time-of-flight (ToF) analysis of the ion cyclotron resonance and by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The experimental and simulated values are in agreement with theoretical predictions [M. Kretzschmar, this issue] when the influence of higher multipole terms is taken into account. 相似文献
19.
Weijun Zheng Soren N. Eustis Xiang Li John M. Nilles Owen C. Thomas Kit H. Bowen Anil K. Kandalam 《Chemical physics letters》2008,462(1-3):35-39
Iron–benzene cluster anions, (n = 1–7, m = 1–4), were generated via laser vaporization and studied using mass spectrometry, anion photoelectron spectroscopy and in one case by density functional theory. Based on these studies, we propose that and Fe1Bz1 as well as and Fe2Bz1 exhibit half-sandwich structures, that and Fe1Bz2, and Fe2Bz2, as well as Fe3Bz2 and Fe4Bz2 are sandwich structures, and that and Fe2Bz3 and larger species form ‘rice-ball’ structures which in each case consist of benzene molecules surrounding an iron cluster core. 相似文献
20.
We perform a computational mapping study of a family of new inorganic species, based on idea of donor–acceptor type bonding between N+ and a ligand L with a terminal electron lone pair. The nitrogen ion is seen as being in an atomic 1D state, with empty 2p acceptor orbitals [I.S.K. Kerkines., A. Papakondylis, A. Mavridis, J. Phys. Chem. A, 2002, 106, 4435]. We consider a series of small ligands, such as PN, CCH−, CCCN−, , and others. Chemical bonding analysis confirms the suggested bonding picture as characteristic for experimentally known and as well as for most of the predicted species. A number of these new compounds is found to be thermodynamically stable with respect to the existing or . They are candidates for new synthetic targets. 相似文献