共查询到20条相似文献,搜索用时 15 毫秒
1.
TOSHIAKI SUZUKI KIMINORI MAEDA TATSUO ARAI KIMIO AKIYAMA SHOZO TERO-KUBOTA 《Molecular physics》2013,111(22):3341-3348
The reaction and spin dynamics of the photocleavage reaction of 2-chloro-2′-acetylnaphthalene were studied by time-resolved FT-EPR and transient absorption (TA) spectroscopy. The photocleavage reaction from both singlet and triplet states was observed by TA and EPR experiments, although the radical cleavage reaction in the excited triplet state is energetically unfavourable. This feature has been explained by the ionic cleavage reaction due to the electro-negativity of the chlorine atoms. The time-resolved FT-EPR spectra were similar to those observed in the bromine substituted compound, 2-BAN, reported in a previous paper. The origin of the electron spin polarization was assigned to the radical triplet pair mechanism (RTPM) and free radical pair mechanism (F-pair RPM) from analysis of the time profiles of the spin polarization. 相似文献
2.
A. San Miguel H. Libotte J.P. Gaspard M. Gauthier J.P. Itié A. Polian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):227-233
The experimental data carried out by M?ssbauer and magnetic resonances investigations of the structural phase transitions
in K2ZnCl4 crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential
V(r), electric field intensity E(r) and electric field gradient tensor, (r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the
model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K sites
obtained by 39K-NMR methods in high temperature incommensurate phase ( Pnam symmetry). The experimental results obtained by M?ssbauer and EPR methods in commensurate phase (Pna21
symmetry) of iron and copper doped K2ZnCl4 crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn2+ site.
Received 3 February 1999 and Received in final form 4 May 1999 相似文献
3.
L.N. Krasnoperov E.N. Chesnokov H. Stark A.R. Ravishankara 《Proceedings of the Combustion Institute》2005,30(1):935-943
Several elementary reactions of formyl radical of combustion importance were studied using pulsed laser photolysis coupled to transient UV–Vis absorption spectroscopy: HCO → H + CO (1), HCO + HCO → products (2), and HCO + CH3 → products (3). One-pass UV absorption, multi-pass UV absorption as well as cavity ring-down spectroscopy in the red spectral region were used to monitor temporal profiles of HCO radical. Reaction (1) was studied over the buffer gas (He) pressure range 0.8–100 bar and the temperature range 498–769 K. Reactions (2a), (2b), (2c), (3a) and (3b) as well as the UV absorption spectrum of HCO, were studied at 298 and 588 K, and the buffer gas (He) pressure of 1 bar. Pulsed laser photolysis (308, 320, and 193 nm) of acetaldehyde, propionaldehyde, and acetone was used to prepare mixtures of free radicals. The second-order rate constant of reaction (1) obtained from the data at 1 bar is: k1(He) = (0.8 ± 0.4) × 10−10exp(−(66.0 ± 3.4) kJ mol−1/RT) cm3 molecule−1 s−1. The HCO dissociation rate constants measured in this work are lower than those reported in the previous direct work. The difference is a factor of 2.2 at the highest temperature of the experiments and a factor of 3.5 at the low end. The experimental data indicate pressure dependence of the rate constant of dissociation of formyl radical 1, which was attributed to the early pressure fall-off expected based on the theory of isolated resonances. The UV absorption spectrum of HCO was revised. The maximum absorption cross-section of HCO is (7.3 ± 1.2) × 10−18 cm2 molecule−1 at 230 nm (temperature independent within the experimental error). The measured rate constants for reactions (2a), (2b), (2c), (3a) and (3b) are: k2 = (3.6 ± 0.8) × 10−11 cm3 molecule−1 s−1 (298 K); k3 = (9.3 ± 2.3) × 10−11 cm3 molecule−1 s−1(298 and 588 K). 相似文献
4.
The transmission characteristics of an air-GaAs interface and the transient absorption and index spectra of the thin, photoexcited surface layer are investigated subsequent to excitation by a femtosecond laser pulse. We find that the total phase change and transmission of a terahertz (THz) probe pulse are dominated by interface effects. This observation has important implications in the interpretation of THz time-domain spectroscopy data of absorbing media. We also observe that the THz pulse apparently arrives at the detector as much as 60 fs earlier when it is transmitted through an optically excited GaAs wafer. This effect is fully explained in terms of a frequency-dependent transmission and phase shift at the air-GaAs interface and is not associated with superluminal propagation. 相似文献
5.
Quenching experiments are shown to provide a convenient tool to check for the presence of triplet mechanism (TM) spin polarisation in time-resolved EPR spectra following laser flash photolysis. The effect of the triplet quenchers, trans-1,3-pentadiene, fumaronitrile, azo-tert-butane and azo-n-butane upon the spectra following laser photolysis of acetone/propan-2-ol and benzophenone/propan-2-ol photosystems show that no TM polarisation is present in the former system but emissive TM is present in the latter. Use of 2,2′-azo-bis[isobutryronitrile] produces an anomalous emissive polarisation upon quenching, which is tentatively attributed to a reversed TM in the triplet sensitised azo-compound. 相似文献
6.
Yu. A. Kozinkin V. V. Pryadchenko L. A. Bugaev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(12):1674-1675
Ab initio modeling is used to analyze the specific near-edge features of the X-ray absorption K spectra of ∼3-nm cobalt nanoparticles. It is established that the observed differences between the spectra of the nanoparticles
and those of bulk cobalt samples are due to contribution from atoms of the nanoparticles’ surface layer, the local environment
of which is considerably different from that of atoms in the bulk of the nanoparticle. It is also established that the local
environment of cobalt atoms in the nanoparticle bulk corresponds to the FCC structure of bulk metal, and the fraction of such
atoms is found to be 65 ± 5%. 相似文献
7.
Simone Draxler Thomas Brust Stephan Malkmus Florian O. Koller Bjrn Heinz Stefan Laimgruber Christine Schulz Steffen Dietrich Karola Rück-Braun Wolfgang Zinth Markus Braun 《Journal of Molecular Liquids》2008,141(3):130
The reaction dynamics of the complete photo cycle, ring-opening (C → E) and ring-closure (E → C), of N-methyl-(6-bromo-1,2-dimethyl-3-indolyl)fulgimide dissolved in acetonitrile are analysed via steady-state and ultrafast spectroscopy using transient absorption in the UV/VIS and mid-IR complemented by ultrafast fluorescence broad-band spectroscopy with a Kerr-gate setup. For the C → E ring-opening reaction induced by light at ~ 550 nm, a time constant of ~ 3 ps was found for the S1 decay and the S0 repopulation. Non-exponential signatures, which occur in the 10 ps time domain, were observed and are assigned to the cooling of hot molecules in the electronic ground state. The E → C reaction dynamics induced by UV-light pulses at 360 nm and 387 nm occur within less than 1 ps and are followed by vibrational cooling on the 10 ps time domain. Thus, both ring-opening and ring-closure reactions are completed within a few picoseconds. From transient IR studies and fluorescence measurements it is concluded that these pericyclic reactions occur from different geometries on the excited state potential energy surface. 相似文献
8.
Johnson SL Heimann PA MacPhee AG Lindenberg AM Monteiro OR Chang Z Lee RW Falcone RW 《Physical review letters》2005,94(5):057407
Even the most basic properties of liquid carbon have long been debated due to the challenge of studying the material at the required high temperature and pressure. Liquid carbon is volatile and thus inherently transient in an unconstrained environment. In this paper we use a new technique of picosecond time-resolved x-ray absorption spectroscopy to study the bonding of liquid carbon at densities near that of the solid. As the density of the liquid increases, we see a change from predominantly sp-bonded atomic sites to a mixture of sp, sp2, and sp3 sites and compare these observations with molecular dynamics simulations. 相似文献
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10.
B. Gauthier-Roy C. Alamichel A. Lecuyer L. Abouaf-Marguin 《Journal of Molecular Spectroscopy》1981,88(1):72-89
Infrared absorption spectra were recorded in the 10-μm region for the three isotopic methyl fluoride molecules 12CH3F, 12CD3F, 13CD3F, in the four rare gas matrices and in nitrogen. The two lowest fundamental modes ν3 (CF stretching) and ν6 (bending) have been systematically studied, as well as the ν2 and ν5 modes of 12CD3F. Relative intensity measurements show that the weak ν6 transition is enhanced by the matrix, compared to its gas-phase value. Frequency measurements yield vibrational shifts which can be compared to a theoretical estimate of the ν3 shift based on the Lennard-Jones-Devonshire cell model. These molecules are almost freely rotating in the matrices and a rotational analysis in the ν3 region brings out quantitative values of the barrier to free rotation as defined in Devonshire's theory. Frequency and relative intensity measurements are also reported for dimeric species. 相似文献
11.
Cho BI Engelhorn K Correa AA Ogitsu T Weber CP Lee HJ Feng J Ni PA Ping Y Nelson AJ Prendergast D Lee RW Falcone RW Heimann PA 《Physical review letters》2011,106(16):167601
We use time-resolved x-ray absorption spectroscopy to investigate the unoccupied electronic density of states of warm dense copper that is produced isochorically through the absorption of an ultrafast optical pulse. The temperature of the superheated electron-hole plasma, which ranges from 4000 to 10?000 K, was determined by comparing the measured x-ray absorption spectrum with a simulation. The electronic structure of warm dense copper is adequately described with the high temperature electronic density of state calculated by the density functional theory. The dynamics of the electron temperature is consistent with a two-temperature model, while a temperature-dependent electron-phonon coupling parameter is necessary. 相似文献
12.
LIII absorption edges of cerium in ternary AuCu3 compounds Ce(Pd1?xMx)3 (M = Ag and Rh) and (Ce1?xYx)Pd3 are presented. We find that Ce in these compounds is mixed valent with nf ? 0.7. The valence V of Ce(Pd1?xRhx)3 becomes concentration independent of V = 3.29 ± 0.02 for x ? 0.18. In Ce1?xYxPd3 we observe the valence to increase up to V = 3.32 ± 0.02 at the highest concentration of Y. We show, that a critical volume, available for the Ce atom, is associated with the concentration independent valence around 3.3. For both systems, linewidths W1, W0 and Δ = E(4f1) ? E(4f0), as derived from LIII double-bump structure, are given. Possible falsifications due to “final states effects” on the valence are discussed. 相似文献
13.
14.
S. Kaschieva K.G. Stefanov D. Karpuzov 《Applied Physics A: Materials Science & Processing》1998,66(5):561-563
2 structures implanted with 50-keV boron ions is studied by deep-level transient spectroscopy (DLTS) measurements. The DLTS
spectra of ion-implanted samples exhibit one peak which corresponds to a deep level located in the forbidden gap of the silicon
matrix at Ec-0.40 eV below the conducting band edge. New additional shallower levels are found in the spectra following bombardment by
high-energy electrons, the peak intensity being dependent on the irradiation dose. The corresponding activation energy of
the created defects, the density of the traps, and the electron-capture cross sections are evaluated.
Received: 27 October 1997/Accepted: 8 December 1997 相似文献
15.
Wodniecki P. Wodniecka B. Kulińska A. Hrynkiewicz A. Z. 《Hyperfine Interactions》2003,151(1-4):291-297
Hyperfine Interactions - The perturbed angular correlation method was applied to follow the oxidation processes in ZrAl and Zr3Al intermetallic compounds. It was found that the limiting temperature... 相似文献
16.
The local structure of LaMnO3 across the Jahn-Teller (JT) transition at T(JT)=750 K was studied by means of x-ray absorption near edge structure and extended x-ray absorption fine structure at the Mn K-edge. Our results indicate a similar electronic local structure for Mn atoms above and below T(JT) and a dynamical tetragonal JT distortion of MnO6 octahedra above T(JT). The structural transition is originated by the ordering of tetragonally distorted octahedra. The entropy content of the transition is analyzed within the framework of the three-state Potts model with nearest neighbor antiferrodistortive coupling. 相似文献
17.
K. Asokan C.L. Dong H.M. Tsai C.L. Chang P. Duran O. Peña 《Solid State Communications》2005,134(12):821-826
Electronic structures of orthorhombic perovskite-type manganites (OM) and hexagonal manganites (HM) are compared by using X-ray absorption near edge structure spectroscopy. This study reveals that the environments around Mn and O ions in both the systems are different. These are reflected primarily in the lifting of degeneracy of the Mn 3d orbitals. Interestingly, the unoccupied Mn 3dx2−y2 orbital in HM is strongly hybridized with O 2p states and appears to be responsible for both long range orderings: ferroelectric ordering at high temperatures and ferromagnetic ordering at low temperatures. 相似文献
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19.
M.T. Klepka K. Lawniczak-Jablonska M. Jablonski 《Journal of Electron Spectroscopy and Related Phenomena》2010,182(3):85-89
Natural ilmenites are used all over the world as raw materials in white pigment (TiO2) production. Besides the FeTiO3 in the raw material many other compounds are present. The chemical compounds based on the minority elements influence quality of the final product and are difficult to identify. The knowledge about chemical bonding of the minor elements enables to properly adjust chemical reactions during production processes and to improve quality of the final product. In this paper the X-ray absorption spectroscopy (XAS) identification of the chemical compounds formed by Mg, Mn and Cr in natural ilmenites originating from different places is presented. 相似文献
20.
A. Gaál I. Bugár I. Capek L. Fialová T. Pálszegi V. Sz?cs A. ?atka F. Uherek 《Laser Physics》2009,19(5):961-968
Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids with particle diameter in range of 10–30 nm is presented. The amplified femtosecond excitation of the surface plasmon resonance band resulted in transient absorption spectra reflecting the electron-phonon relaxation dynamics, which takes place on the early picosecond time scale. The monitored band with enhanced absorption in the 490–540 nm spectral range exhibited red-shift with increasing pump fluency from 0.4 mJ/cm2 to the 1.5 mJ/cm2 level. The growth of the relaxation time with increasing pump fluency reveals the temperature dependent relaxation dynamics caused by the nanometer sized electron confinement in the case of silver. This effect was confirmed also by identification of the relaxation time dependence on the particle diameter at constant pump fluency. The complex experimental results revealed nonlinearities both in the laser excitation and electron relaxation processes. 相似文献