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81.
Coherent anti-Stokes Raman scattering (CARS) spectra of excited molecules as well as Shpolskii spectra provide information about geometry changes between ground and excited states. Vibrational frequencies and relative intensities from recently obtained CARS spectra of the chrysene S1 and T1 state and earlier observed Shpolskii spectra are interpreted in terms of molecular geometry and force-field changes by means of quantum-chemical consistent force field (QCFF) and Franck-Condon factor calculations. The comparison of observed and calculated relative intensities indicates a coupling between the S1 and S2 state enhancing some of the vibrational radiative singlet transitions both in absorption and fluorescence spectra whereas within the phosphorescence spectra proportionality to calculated Franck-Condon factors is obeyed. The T1 state is the more loosely bound state and its geometry change is different from that of the S1 state. The resonance CARS transitions in the S1 state are assigned to totally symmetric vibrations getting their intensity by a coupling scheme analogous to the A term of the resonance Raman effect: the relative intensity of a transition is shown to be proportional to the Franck-Condon factor to the higher excited state and to the squared vibrational frequency. Using this relation this state can be identified by means of its finger-print-like intensity pattern. 相似文献
82.
83.
For a gaussian broadband radiation field (multimode laser without phase-correlation) the bleaching behaviour of a homogeneously broadened two level system is investigated in dependence on the spectral width (δυ) of the field. Taking into consideration the coherent mode-interaction, originating from the nonstationary reaction of population inversion on the fluctuations of the radiation field, a decrease of the bleaching effect results as soon as the spectral width δυ becomes larger than ⊥1 = 1/T1 with T1 the longitudinal relaxation time of the molecular transition concerned. Neglecting this effect in the analysis of broadband bleaching measurements can result in the unjustified assumption of an inhomogeneous broadening of the spectral band under consideration, which has consequences on the magnitude of the molecular absorption cross-section derived from these measurements. 相似文献
84.
We present a novel, simple asymptotic expansion for the spectrum of radiation that is backscattered from a laser by a counterpropagating (or copropagating) electron. The solutions are presented in such a way that they explicitly show the relative merit of using an intense laser and of an energetic electron beam in x-ray production in the single particle regime. Simple scaling laws are given. 相似文献
85.
Single-element, planar transducers have been fabricated using electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 80/20 mol% copolymers with different electron dosage. Electrical field-induced strain response of copolymer film with 100 Mrad dosage has been studied at 5 kHz and the electrostrictive coefficient was calculated. The transmitting response of the air-backing and epoxy-backing transducers was evaluated with the application of high DC bias voltages. Clear ultrasonic amplitudes and high frequency spectrum (>20 MHz) were observed when driven from a standard ultrasonic voltage source through a decoupling circuit. It has also showed that larger generation of ultrasonic waves will be induced under high DC bias field, which is due to the increase of induced d(33) piezoelectric coefficient. Two different polar bias voltages, positive and negative, were applied to the transducers and inverse waveforms were received, which was coincident with the theoretical analysis of the strain response of electrostrictive film. 相似文献
86.
Lau JK Wong CH Ng PS Siu FM Ma NL Tsang CW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3383-3396
The potassium cation affinities (PCAs) of 136 ligands (20 classes) in the gas phase were established by hybrid density functional theory calculations (B3-LYP with the 6-311+G(3df,2p) basis set). For these 136 ligands, 70 experimental values are available for comparison. Except for five specific PCA values-those of phenylalanine, cytosine, guanine, adenine (kinetic-method measurement), and Me(2)SO (by high-pressure mass spectrometric equilibrium measurement)-our theoretical estimates and the experimental affinities are in excellent agreement (mean absolute deviation (MAD) of 4.5 kJ mol(-1)). Comparisons with previously reported theoretical PCAs are also made. The effect of substituents on the modes of binding and the PCAs of unsubstituted parent ligands are discussed. Linear relations between Li+/Na+ and K+ affinities suggest that for the wide range of ligands studied here, the nature of binding between the cations and a given ligand is similar, and this allows the estimation of PCAs from known Li+ and/or Na+ affinities. Furthermore, empirical equations relating the PCAs of ligands with their dipole moments, polarizabilities (or molecular weights), and the number of binding sites were established. Such equations offer a simple method for estimating the PCAs of ligands not included in the present study. 相似文献
87.
The synthesis of the first mesogenic hexaalkoxybenzo[b]triphenylene derivative is reported; this compound exhibits a broad columnar liquid crystal phase at temperatures only slightly above room temperature. 相似文献
88.
89.
We report on an intracavity optical parametric oscillator (OPO) placed within a compact diode-pumped Nd:YALO laser cavity. This OPO utilizes a pair of KTP crystals, which are diffusion bonded together in a walk-off-compensated configuration. We have generated up to 21.4 W of 2-mum radiation, operating in a few-kilohertz range. 相似文献
90.
To improve the productivities of an automated container terminal, it is important to schedule different types of handling
equipment in an integrated way. A mixed-integer programming model, which considers various constraints related to the integrated
operations between different types of handling equipment, is formulated. A heuristic algorithm, called multi-layer genetic
algorithm (MLGA) is developed with a view to overcome the computation difficulty for solving the mathematical model. A numerical
experimentation is carried out in order to evaluate the performance of the algorithm. 相似文献