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101.
Yasuyuki Kowaka Noritaka Ashizawa Hitoshi Goto Umpei Nagashima Masaaki Baba 《Journal of Molecular Spectroscopy》2010,260(1):72-9519
A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S1 ← S0 transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D2h symmetry. We determined the geometrical structure in the S0 state by ab initio theoretical calculation at the RHF/6-311+G(d,p) level, which yielded rotational constant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S11B2u state is very slow. The rate of internal conversion (IC) is also inferred to be small because the fluorescence quantum yield is high. The rotational constants of the S11B2u state were very similar to those of the S01Ag state. The slow internal conversion (IC) at the S1 zero-vibrational level is attributed to a small structural change upon electronic transition. 相似文献
102.
Vinayak Rane 《Molecular physics》2013,111(1):157-165
Time-resolved EPR studies of the hydrogen abstraction reaction of photoexcited xanthone in 2-propanol were carried out as a function of the concentration of xanthone and the sample temperature. The temperature was varied from 22°C to about ?30°C, and the concentration from about 0.2 to 4.0?mM. At low temperature or concentration, the observed spectra of the xanthone ketyl radical and the propan-2-olyl radical could be simulated as a superposition of a hyperfine-independent component due to the emissive triplet mechanism and a hyperfine-dependent component due to the S–T0 radical pair mechanism. However, with an increase in the concentration of xanthone, the relative contribution of TM decreases, and, concomitantly, the net absorptive component of only the xanthone ketyl radical increases. As the spin polarisation mechanisms do not predict any concentration dependence, this unusual behaviour is explained by invoking the enhancement of the spin–lattice relaxation rates due to Heisenberg spin exchange occurring at high local concentrations of the radicals. The net absorptive signal is attributed to thermally equilibrated radicals. The observed temperature dependence of the spin polarisation behaviour is similarly explained. The origin of the net absorptive signal in the TREPR spectra of the acetone?2-propanol system is also attributed to thermally equilibrated radicals. The self-quenching mechanism of xanthone is proposed to be an electron-transfer reaction from an excited xanthone molecule to another xanthone in the ground state. 相似文献
103.
In this contribution we report studies on the nature of binding of a small ligand/drug Nile blue (NB) with sodium dodecyl
sulfate (SDS) micelles, bis-(2-ethylehexyl) sulfosuccinate (AOT)/isooctane reverse micelles (RM) and a genomic DNA extracted
from Salmon sperm. With detailed steady state and picosecond resolved optical spectroscopic techniques, we examined the fluorescence
quenching of the ligand upon complexation with the SDS monomers and DNA. Polarization analyzed picosecond-resolved fluorescence
measurements reveal geometrical restriction on the probe in SDS micelles, AOT-RM and DNA. Steady state and time resolved studies
on the probe in nanocages of AOT RM with various degrees of hydration (w0) reveal the existence of NB as two distinct species namely, neutral and cationic. This study confirms that the emission of
NB in aqueous micelles and DNA solution is due to the cationic form of the drug. Our experiments clearly identified non-specific
electrostatic and intercalative modes of interaction of the probe with the DNA at lower and higher DNA concentrations respectively.
The nature of binding of NB in presence of the DNA and SDS micelles reveals that the binding affinity of the probe is higher
with the micelles than with the DNA. The complex rigidity of NB with DNA and its fluorescence quenching with DNA elucidate
a strong recognition mechanism between NB and DNA. 相似文献
104.
Davor Pavuna Daniel Ariosa Dominique Cloetta Claudia Cancellieri Mike Abrecht 《Pramana》2008,70(2):237-243
Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T
c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped
in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x
Sr
x
CuO4 (LSCO) films we almost double T
c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES
data under tensile strain exhibit the dispersion that is three-dimensional, yet T
c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T
c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established
the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual
lattice of cuprates is like a ‘Napoleon-cake’, i.e. rigid CuO2 planes alternating with softer ‘reservoir’, that distort differently under strain, our data rule out all oversimplified two-dimensional
(rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T
c.
相似文献
105.
激光诱导Co等离子体电子温度的时间空间演化特性研究 总被引:2,自引:1,他引:1
本文在380~500 nm波长范围内测定了激光烧蚀Co等离子体中Co原子的时间和空间分辨发射光谱.由发射光谱线的强度和Stark展宽分别计算了等离子体电子温度和电子密度,并由实验结果讨论了激光等离子体中电子温度的时间和空间演化特性.实验结果表明,当延时在100~1000 ns范围内变化时,相应的电子温度Te范围为8000~25000 K;当距离靶表面0~1.8 mm范围内变化时,相应的电子温度Te范围为13000~25000 K,电子温度在激光束方向上的分布具有很好的对称性. 相似文献
106.
Sergei G. Kruglik Jean‐Christophe Lambry Jean‐Louis Martin Marten H. Vos Michel Negrerie 《Journal of Raman spectroscopy : JRS》2011,42(3):265-275
We describe a pump–probe Raman spectrometer based on a femtosecond Ti:sapphire laser, an optical parametric generator and two optical parametric amplifiers for time‐resolved studies, with emphasis on the structural dynamics in heme proteins. The system provides a 100‐fs pump pulse tunable in the range 500–600 nm and a transform‐limited sub‐picosecond probe pulse tunable in the range 390–450 nm. The spectrometer has spectral (25 cm−1) and temporal (∼0.7 ps) resolutions which constitute an effective compromise for identifying transient heme protein species and for following their structural evolution by spontaneous Raman scattering in the time range 0.5 ps to 2 ns. This apparatus was applied to time‐resolved studies of a broad range of heme proteins, monitoring the primary dynamics of photoinduced heme coordination state and structural changes, its interaction with protein side‐chains and diatomic gaseous ligands, as well as heme vibrational cooling. The treatment of transient Raman spectra is described in detail, and the advantages and shortcomings of spontaneous resonance Raman spectroscopy for ultrafast heme proteins studies are discussed. We demonstrate the efficiency of the constructed spectrometer by measuring Raman spectra in the sub‐picosecond and picosecond time ranges for the oxygen‐storage heme protein myoglobin and for the oxygen‐sensor heme protein FixLH in interaction with the diatomic gaseous ligands CO, NO, and O2. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
107.
Time‐resolved coherent anti‐Stokes Raman scattering (CARS) impulsively excited by a supercontinuum (SC) is investigated. We show that it is critical to optimize the temporal overlapping of the constituent solitons of a SC in order to impulsively excite vibrational modes over a broad frequency range. The cross‐correlation frequency‐resolved optical gating technique is utilized to retrieve the optical response function of molecules under SC impulsive excitation, and background‐free CARS with spectral resolution significantly better than the bandwidth of the probe pulses is achieved. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
108.
Yeny A. Tobon Denis Bormann Aurlien Canizares Nicole Raimboux Patrick Simon 《Journal of Raman spectroscopy : JRS》2011,42(5):1109-1113
A time‐resolved intensified charge coupled device‐based Raman microspectrometer system dedicated to the study of solid samples is described, offering good optical, temporal and spatial resolution. The advantages of this approach are demonstrated on Al2O3:Cr3+, obtaining for the first time the temporal evolution of the excited state transition Ē → 2Ā. Moreover, the time dependence of the luminescence due to the chromium ion was also determined by the same Raman device. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
109.
Natural products often possess various spin systems consisting of a methine group directly bonded to a methyl group (e.g. –CHa–CHb(CH3)–CHc–). The methine proton Hb splits into a broadened multiplet by coupling with several vicinal protons, rendering analysis difficult of nJC–H with respect to Hb in the J‐resolved HMBC‐1. In purpose of the reliable and easy measurements of nJC–H and nJH–H in the aforesaid spin system, we have developed a new technique, named BASHD‐J‐resolved‐HMBC. This method incorporates band selective homo decoupled pulse and J‐scaling pulse into HMBC. In this method, high resolution cross peaks can be observed along the F1 axis by J‐scaling pulse, and band selective homo decoupled pulse simplified multiplet signals. Determinations of nJC–H and nJH–H of multiplet signals can easily be performed using the proposed pulse sequence. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
110.
A. O. Kostetskyi Yu. P. Piryatinski A. B. Verbitsky P. M. Lutsyk A. Rozhin 《Molecular Crystals and Liquid Crystals》2020,697(1):31-48
AbstractTime resolved emission spectra (TRES), 3D maps of photoluminescence excitation-emission (PLE maps), 3D maps of TRES, and kinetics of photoluminescence (PL) spectra of natural and synthetic melanin, as well as melanin composites with surfactant, sodium dodecyl benzenesulfonate, have been studied. The kinetics of PL and TRES for the melanin and the composites were investigated at low temperatures that allowed to discuss melanin’s intermolecular complexation, nano-aggregation and formation of charge transfer states. Particularly, the radiation of Frenkel excitons from fragments of different degrees of conjugation that are the parts of molecular nanodisks of melanin is observed. Furthermore, charge transfer excitons (CT-excitons) can be formed and observed at both room and helium temperatures. Some bands in the PL spectra of melanin, depending on temperature, behave like excimer radiation. The studies are aiming to understand the electronic properties of various melanins, particularly natural ones. 相似文献