Phonon-driven ultrafast exciton dissociation at donor-acceptor polymer heterojunctions

A quantum-dynamical analysis of exciton dissociation at polymer heterojunctions is presented, using a hierarchical electron-phonon model parametrized for three electronic states and 28 vibrational modes. Two representative interfacial configurations are considered, both of which exhibit an ultrafast exciton decay. The efficiency of the process depends critically on the presence of intermediate bridge states, and on the dynamical interplay of high- vs low-frequency phonon modes. The ultrafast, highly nonequilibrium dynamics is consistent with time-resolved spectroscopic observations.     

不同极性溶液中MEH-PPV链内激子扩散的研究

本文采用飞秒时间分辨瞬态光栅技术研究了MEH-PPV在不同极性溶液中的内激子扩散行为. 采用宽带连续白光同时探测瞬态吸收和瞬态光栅信息. 系统地研究了MEH-PPV的振动失相行为以及单激子弛豫和粒子数弛豫动力学. 结果表明,在极性较大的溶剂中,样品溶液的弛豫扩散过程会加快.     

Fundamental absorption spectra of solid hydrogen

Absorption spectra of solid H₂ and D₂ are measured in the range 10–40 eV at 2K for the first time, using synchrotron radiation. The spectra can be divided into two components; exciton and interband transitions. The exciton absorption consists of bands corresponding to molecular transitions, and vibrational structures are observed in the first exciton band of solid H₂.     

Triplet exciton energy and the magnitude of the charge-transfer interaction inside dimers in the Alkali-TCNQ salts

The optical absorption spectra of several crystalline anion radiacal salts have been analyzed recently within the frame of the model Hamiltonian of electrons and intramolecular excitons and vibrations in the limit of strong interaction of the excitonic and vibrational motions with the unpaired electrons. In the present work the magnitude of the intermolecular charge transfer interaction inside dimers in the Alkali TCNQ salts is deduced from the knowledge of the experimental triplet exciton energy and the constants characterizing the electronic, excitonic and vibrational properties of TCNQ molecules. Perturbation calculation is used to derive a formula for the triplet exciton energy.     

Excitons in silicon nanocrystallites

Recombination and binding energies of excitons in nanocrystalline silicon quantum dots are calculated within the effective mass approximation including the effects of the induced electrostatic polarization. The calculated exciton recombination energies compare well with other calculations and with the results from photoluminescence measurements in porous silicon. The calculated exciton binding energies are far larger than the bulk exciton binding energy and show substantial dependence on the matrix that surrounds the nanocrystallites. A model is proposed that explains the main orange-red, blue and infrared luminescence peaks of porous silicon within a simple unified framework.     

Study on infrared multiphoton excitation of the linear triatomic molecule by the Lie-algebra approach

Infrared multiphoton vibrational excitation of the linear triatomic molecule has been studied using the quadratic anharmonic Lie-algebra model, unitary transformations, and Magnus approximation. An explicit Lie-algebra expression for the vibrational transition probability is obtained by using a Lie-algebra approach. The infrared multiphoton vibrational excitation of the DCN molecule is discussed as an example.     

Hydrogen bond dynamics probed with ultrafast infrared heterodyne-detected multidimensional vibrational stimulated echoes

Hydrogen bond dynamics are explicated with exceptional detail using multidimensional infrared vibrational echo correlation spectroscopy with full phase information. Probing the hydroxyl stretch of methanol-OD oligomers in CCl4, the dynamics of the evolving hydrogen bonded network are measured with ultrashort (<50 fs) pulses. The data along with detailed model calculations demonstrate that vibrational relaxation leads to selective hydrogen bond breaking on the red side of the spectrum (strongest hydrogen bonds) and the production of singly hydrogen bonded photoproducts.     

Electroreflectance vibrational spectroscopy: A new surface analysis technique using diode lasers

A new infrared technique to measure the vibrational spectra of adsorbed molecules is introduced. An Infrared active mode of an oriented molecule has a first order Stark effect. Therefore, infrared absorption by oriented adsorbed molecules is modulated by an alternating electric field. The spectra is obtained by measuring this using a diode laser. The advantages and limitations of Electroreflectance Vibrational Spectroscopy (EVS) are discussed. We calculate the Stark tuning rate and consequent signal amplitude for a number of diatomic molecules. Measurements of diode laser Intensity noise are used to estimate the signal to noise ratio for comparison with other techniques.     

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

Mixed water aerosols are important components of planetary and lunar atmospheres. In this work, we use rapid-scan Fourier transform infrared (IR) spectroscopy to study solid ammonia–water and acetylene–water aerosol particles formed in a bath gas cooling cell at 78 K. With this set-up, we record time-dependent extinction spectra of particle ensembles in the mid-IR to monitor changes to the internal structure of the aerosol particles. Both ammonia–water and acetylene–water were found to form molecularly mixed structures. The mixing is observed by monitoring the profile for the ammonia ν₂ band and the acetylene ν₅ band, both of which are sensitive to particle properties. Depending on the injection conditions, the mixed particles form either immediately after sample injection or after a short mixing period of several tens of minutes. We confirm the formation of mixed particles by comparing the experimental spectra with spectra calculated with the vibrational exciton model.     

Hyperfine Level Dependence of the Pressure Broadening of CH(3)I Rotational Transitions in the v(6) = 1 Vibrational State

We studied the hyperfine components of the (J = 10-9, Kl = 9) rotational transition in the v(6) = 1 excited vibrational state of CH(3)I, using collinear infrared and mm-wave radiations. The Doppler-free double-resonance technique allowed an accurate determination of the collisional broadening parameters for all the hyperfine components. An evident dependence on the F quantum number was observed and this result is perfectly consistent with a theoretical model allowing calculations of collisional broadening and coupling for the hyperfine components. Copyright 2000 Academic Press.     

Vibrational spectra of a GaS single crystal

The Raman and infrared active long wavelength phonons of a GaS single crystal were studied at different temperatures in the 10–600 cm^?1 range. Properly polarized Raman spectra could be obtained with the 4880 Å exciting line and the previous assignment of the E_1g modes controversed recently could be confirmed. Infrared spectra were recorded in the 30–600 cm^?1 region. The vibrational frequencies of the crystal were also calculated using a method developed by Wieting and six new frequencies corresponding to infrared and Raman inactive modes have been proposed.We have observed that the degree of leakage of scattered intensity in unallowed polarizations increases when the wavelength of the exciting line moves off the exciton absorption front. The phonon at 74 cm^?1 was particularly sensitive and the question of the antiresonant behaviour of this compound is raised.     

聚噻吩中双电子极化子附近的二维局域振动模

将聚噻吩的一维SSH孤子模型推广到二维平面,研究了聚噻吩双电子极化子附近的二维局域振动模.计算结果表明双电子极化子附近存在15个局域振动模,其中4个奇宇称模与4条强红外吸收谱线1020,1120,1200,1323cm^-1相对应,4个偶宇称模恰与4条Raman吸收峰700,1047,1175,1220cm^-1一致. 关键词：     

IR Absorption,Raman Scattering,and IR-Vis Sum-Frequency Generation Spectroscopy as Quantitative Probes of Surface Structure

Abstract:Vibrational spectroscopy is a valuable quantitative tool for the determination of structure at surfaces. Various techniques may be applicable and useful, depending on what is available, the transparency of the substrates, the need for in situ probes, and the degree of interfacial specificity required. We examine and compare signals in infrared absorption, Raman scattering, and vibrational sum-frequency generation spectroscopy to the underlying molecular response. In all of these experiments, varying the beam polarizations enables the orientation of specific chemical functional groups to be determined. However, the sensitivity of each technique is directly connected to the manner in which the molecular response manifests itself in the measured signal. Starting with simple distributions of a single vibrational mode, leading up to multiple vibrational bands in more complex orientation distributions, we compare these three techniques in terms of their sensitivity to features of the molecular orientation distribution. This review is aimed at guiding planned experiments when multiple techniques are available for surface structural analysis.     

Detecting spatially localized excitons in InGaN quantum well structures with a micro-photoluminescence technique

Spatially localized excitons are observed in InGaN quantum well structures at 4 K by using a micro-photoluminescence (PL) technique. By combining PL and nano-lithographic techniques, we are able to detect PL signals with a 0.2 μm spatial resolution. A sharp PL line (linewidth of <0.4 meV) is clearly obtained, which originates from a single localized exciton induced by a quantum dot like a local potential minimum position. Sharp PL spectra detected in three QWs with different indium compositions confirm that there are exciton localization effects in quantum wells in the blue-green (about 2.60 eV, 477 nm) to purple (about 3.05 eV, 406 nm) regions.     

超冷铯分子纯长程态转动常数的精密测量

利用调制的俘获损耗光谱技术实验测量了超冷铯分子纯长程0_g^-态的高分辨光谱. 采用双光缔合光谱技术构建了精确的频率差参考信号, 对转动能级的共振频率间隔进行了精确的标定, 获得了转动能级频率间隔与转动量子数的关系. 通过将实验数据拟合到非刚性转动模型, 获得了超冷铯分子纯长程0_g^-态不同振动态的转动常数. 实验结果表明转动常数随振动量子数的增加而线性减小, 线性递减率为-0.41 MHz±0.01 MHz. 关键词： 双光缔合光谱技术 超冷铯分子 转动常数 纯长程态     

Vibrational and electronic spectral analysis of 2,3-pyrazinedicarboxylic acid: A combined experimental and theoretical study

Fourier transform infrared and Raman spectra of 2,3-pyrazinedicarboxylic acid were recorded and analyzed using density functional theory. The complete assignments of the anharmonic vibrational modes have been performed based on potential energy distribution. The anharmonic frequencies were computed using vibrational second-order perturbation theory as well as vibrational self-consistent field and correlation corrected vibrational self-consistent field methods. Mode–mode coupling strength is also estimated using two-mode representation of quartic force field approximation. The intra- and intermolecular interactions were also studied in the dimer and trimer forms of the title molecule. The ultraviolet–visible absorption spectra in ethanol, methanol, and acetonitrile solvents were recorded and analyzed using time-dependent density functional theory involving the polarization continuum model. The observed and calculated results are well comparable. Molecular electrostatic potential and the highest occupied and the lowest unoccupied molecular orbital analyses are also reported.     

Femtosecond vibrational dynamics of self-trapping in a quasi-one-dimensional system

We have directly time resolved the lattice motions associated with the formation of the self-trapped exciton in the quasi-one-dimensional system [Pt(en)(2)] [Pt(en)2Br2];(PF6)(4) ( en = ethylene-diamine, C2H8N2), using femtosecond impulsive excitation techniques. A strongly damped, low-frequency wave packet modulation at approximately 110 cm(-1) accompanies the formation of the self-trapped exciton on a approximately 200 fs time scale following excitation of the intervalence charge-transfer transition. Coherent oscillations at the ground state vibrational frequency and its harmonics are also detected.     

Double pulsed holography used to investigate noisy brakes

The vibrational characteristics of a noisy passenger car disc brake have been studied using the double pulsed holographic technique which has been developed to allow three orthogonal visual images of a vibrating brake system to be recorded simultaneously. These images show the disc to be vibrating in a bending mode whereas the pad is seen to be excited in a variety of modes such as bending, torsion, and often a combination of both. The development of the technique includes alternative ways of triggering the laser and typical results from the application of these differing methods are also included along with mechanical signals which confirm the visual interpretations. Final results, using a laser trigger delay technique, show that the disc mode waveform rotates about the disc at a rate equivalent to the frequency of vibration divided by the diametral mode order. Early work on a passenger car drum brake is also introduced, this complementing commercial ‘noise fix’ solutions and a proposed theoretical model.     

The Features of Infrared Absorption of the Protein Molecules in the Living System

We utilize a vibron-soliton model for amide-I vibrational quanta interacting with optical phonons to study the feature of infrared absorption of the protein molecules with finite temperatuse.The self-trapping of amide-Ik vibrational quantum results in red shift of the main peak and largely anomalous band to occur in the infrared absorption for the protein molecules.utilizing the concise model of vibron and improved theory of color centers we have given theoretically the value of red shifts of the main peak and the intensity of anomalous band in infrared absorption,respectively,the latter reduces with increasing temperature which is consistent with the experimental result.