Direct measurement of S-branch N(2)-H(2) Raman linewidths using time-resolved pure rotational coherent anti-Stokes Raman spectroscopy

S-branch N(2)-H(2) Raman linewidths have been measured in the temperature region 294-1466 K using time-resolved dual-broadband picosecond pure rotational coherent anti-Stokes Raman spectroscopy (RCARS). Data are extracted by mapping the dephasing rates of the CARS signal temporal decay. The J-dependent coherence decays are detected in the time domain by following the individual spectral lines as a function of probe delay. The linewidth data set was employed in spectral fits of N(2) RCARS spectra recorded in binary mixtures of N(2) and H(2) at calibrated temperature conditions up to 661 K using a standard nanosecond RCARS setup. In this region, the set shows a deviation of less than 2% in comparison with thermocouples. The results provide useful knowledge for the applicability of N(2) CARS thermometry on the fuel-side of H(2) diffusion flames.     

Time-resolved coherent anti-Stokes Raman-scattering measurements of I2 in solid Kr: vibrational dephasing on the ground electronic state at 2.6-32 K

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out for iodine (I2) in solid krypton matrices. The dependence of vibrational dephasing time on temperature and vibrational quantum number v is studied. The v dependence is approximately quadratic, while the temperature dependence of both vibrational dephasing and spectral shift, although weak, fits the exponential form characteristic of dephasing by pseudolocal phonons. The analysis of the data indicates that the frequency of the pseudolocal phonons is approximately 30 cm(-1). The longest dephasing times are observed for v = 2 being approximately 300 ps and limited by inhomogeneous broadening. An increase in the dephasing rate of v = 2 as the temperature is lowered to T = 2.6 K is taken as a clear indication of lattice-strain-induced inhomogeneity of the ensemble coherence.     

Femtosecond dephasing studies of dye molecules in a polymer host

A femtosecond three-pulse scattering technique is used to observe dephasing of the lowest electronic transition of cresyl violet in poly-methyl methacrylate. The transition from inhomogeneous to homogeneous broadening is studied as temperature is increased front 15 to 290 K.     

High-resolution solid-state 2H NMR spectroscopy of polymorphs of glycine

High-resolution solid-state (2)H MAS NMR studies of the α and γ polymorphs of fully deuterated glycine (glycine-d(5)) are reported. Analysis of spinning sideband patterns is used to determine the (2)H quadrupole interaction parameters, and is shown to yield good agreement with the corresponding parameters determined from single-crystal (2)H NMR measurements (the maximum deviation in quadrupole coupling constants determined from these two approaches is only 1%). From analysis of simulated (2)H MAS NMR sideband patterns as a function of reorientational jump frequency (κ) for the -N(+)D(3) group in glycine-d(5), the experimentally observed differences in the (2)H MAS NMR spectrum for the -N(+)D(3) deutrons in the α and γ polymorphs is attributed to differences in the rate of reorientation of the -N(+)D(3) group. These simulations show severe broadening of the (2)H MAS NMR signal in the intermediate motion regime, suggesting that deuterons undergoing reorientational motions at rates in the range κ ≈ 10(4)-10(6) s(-1) are likely to be undetectable in (2)H MAS NMR measurements for materials with natural isotopic abundances. The (1)H NMR chemical shifts for the α and γ polymorphs of glycine have been determined from the (2)H MAS NMR results, taking into account the known second-order shift. Further quantum mechanical calculations of (2)H quadrupole interaction parameters and (1)H chemical shifts reveal the structural dependence of these parameters in the two polymorphs and suggest that the existence of two short intermolecular C-H···O contacts for one of the H atoms of the >CH(2) group in the α polymorph have a significant influence on the (2)H quadrupole coupling and (1)H chemical shift for this site.     

Shaping femtosecond coherent anti-Stokes Raman spectra using optimal control theory

Optimal control theory is used to tailor laser pulses which enhance a femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) spectrum in a certain frequency range. For this aim the optimal control theory has to be applied to a target state distributed in time. Explicit control mechanisms are given for shaping either the Stokes or the probe pulse in the four-wave mixing process. A simple molecule for which highly accurate potential energy surfaces are available, namely molecular iodine, is used to test the procedure. This approach of controlling vibrational motion and delivering higher intensities to certain frequency ranges might also be important for the improvement of CARS microscopy.     

Femtosecond/picosecond time-resolved fluorescence study of hydrophilic polymer fine particles

Femtosecond/picosecond time-resolved fluorescence study of hydrophilic polymer fine particles (polyacrylamide, PAAm) was reported. Ultrafast fluorescence dynamics of polymer/water solution was monitored using a fluorescent probe molecule (C153). In the femtosecond time-resolved fluorescence measurement at 480 nm, slowly decay components having lifetimes of tau(1) approximately 53 ps and tau(2) approximately 5 ns were observed in addition to rapid fluorescence decay. Picosecond time-resolved fluorescence spectra of C153/PAAm/H2O solution were also measured. In the time-resolved fluorescence spectra of C153/PAAm/H2O, a peak shift from 490 to 515 nm was measured, which can be assigned to the solvation dynamics of polymer fine particles. The fluorescence peak shift was related to the solvation response function and two time constants were determined (tau(3) approximately 50 ps and tau(4) approximately 467 ps). Therefore, the tau(1) component observed in the femtosecond time-resolved fluorescence measurement was assigned to the solvation dynamics that was observed only in the presence of polymer fine particles. Rotational diffusion measurements were also carried out on the basis of the picosecond time-resolved fluorescence spectra. In the C153/PAAm/H2O solution, anisotropy decay having two different time constants was also derived (tau(6) approximately 76 ps and tau(7) approximately 676 ps), indicating the presence of two different microscopic molecular environments around the polymer surface. Using the Stokes-Einstein-Debye (SED) equation, microscopic viscosity around the polymer surface was evaluated. For the area that gave a rotational diffusion time of tau(6) approximately 76 ps, the calculated viscosity is approximately 1.1 cP and for tau(7) approximately 676 ps, it is approximately 10 cP. The calculated viscosity values clearly revealed that there are two different molecular environments around the polyacrylamide fine particles.     

利用时间分辨相干反斯托克斯拉曼散射技术研究光催化产氢反应动力学

基于飞秒再生放大器及飞秒光学参量放大器输出的激光脉冲, 搭建了宽带时间分辨相干反斯托克斯拉曼散射(CARS)测试装置, 并利用该装置研究了氢气与空气混合气体中氢气的相对含量, 探测相对延时与CARS光谱之间的关系. 通过调整延时, 获得了无非共振背景干扰的氢气CARS信号. 实验中测得的CARS信号强度与氢气浓度(分压)的平方呈良好的线性关系, 符合CARS理论预测. 同时测得的实验数据的信噪比表明: 在当前的实验条件下, 在氢气与空气混合气的总压为0.1 MPa时, 该装置可以对氢气的浓度进行测量, 且其检测极限可低至0.2%. 本文还利用该装置对三联吡啶苯乙炔Pt 配合物-Co 配合物-三乙醇胺(TEOA)的三元化学催化体系的产氢动力学行为进行了研究, 通过改变pH值讨论了该催化体系的产氢动力学机制. 结果表明过高的质子浓度会降低体系的产氢效率, 这可能是因为在酸性条件下, 作为质子和电子供体的三乙醇胺分解被抑制, 电子供应中断, 导致产氢反应的停止.     

Side-on bound dinitrogen complex of zirconium supported by a P2N2 macrocyclic ligand

Reduction of [P 2N 2]ZrCl 2 (where P 2N 2 = PhP(CH 2SiMe 2NSiMe 2CH 2) 2PPh) by KC 8 under N 2 generates the dinuclear dinitrogen complex ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2) and impurities in varying yields depending on the solvent and temperature. The toluene complex [P 2N 2]Zr(eta (6)-C 7H 8) along with a dinuclear species with bridging PC 6H 5 groups is observable. Also observable in the crude reaction mixtures is the mu-oxodiazenido derivative, ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2H 2)(mu-O), due to reaction with trace H 2O. This paper reports the full details of the preparation of ([P 2N 2]Zr) 2(mu-eta (2):eta (2)-N 2) including an improved method that involves reduction at low temperatures in a tetrahydrofuran solvent. Also reported is a reproducible synthesis of the oxodiazenido complex along with the X-ray structures of the dinitrogen complex and the oxodiazenido derivative.     

Origin of the nonexponential dynamics of excited-state proton transfer in wt-green fluorescent protein

We used an inhomogeneous excited-state proton-transfer kinetics model to explain the origin of the non-exponential time-resolved emission of the A-band of wt-green fluorescence protein. The calculated fit is rather good for both H 2O and D 2O samples in a wide temperature range of 80-229 K. We attribute the inhomogeneous kinetics to the distance dependence of the excited-state proton-transfer rate between the proton donor (the hydroxyl group of the chromophore) and the oxygen of a nearby water molecule.     

Comment: Comment on saturation effects in high-resolution coherent anti-stokes Raman spectroscopy of a pulsed molecular beam

Saturation broadening in coherent anti-stokes Raman spectroscopy (CARS) is analyzed under conditions where relaxation effects are negligible by solving the appropriate Bloch equations exactly. The present analysis extends that previously given by Duncan, Oesterlin, König and Byer, who experimentally observed saturation broadening in high-resolution CARS.     

Quantum theory of time-resolved femtosecond stimulated Raman spectroscopy: direct versus cascade processes and application to CDCl3

We present a quantum mechanical wave packet treatment of time-resolved femtosecond stimulated Raman spectroscopy (FSRS), or two-dimensional (2D) FSRS, where a vibrational coherence is initiated with an impulsive Raman pump which is subsequently probed by FSRS. It complements the recent classical treatment by Mehlenbacher et al. [J. Chem. Phys. 131, 244512 (2009)]. In this 2D-FSRS, two processes can occur concurrently but with different intensities: a direct fifth-order process taking place on one molecule, and a cascade process comprising two third-order processes on two different molecules. The cascade process comprises a parallel and a sequential cascade. The theory is applied to the 2D-FSRS of CDCl(3) where calculations showed that: (a) the cascade process is stronger than the direct fifth-order process by one order of magnitude, (b) the sidebands assigned to C-Cl E and A(1) bends, observed on both sides of the Stokes C-D stretch frequency, are not due to anharmonic coupling between the C-D stretch and the C-Cl bends, but are instead due to the coherent anti-Stokes Raman spectroscopy (CARS) and coherent Stokes Raman spectroscopy (CSRS) fields produced in the first step of the cascade process, (c) for each delay time between the femtosecond impulsive pump and FSRS probe pulses, the line shape of the sidebands shows an inversion symmetry about the C-D stretch frequency, and this is due to the 180(°) phase difference between the CARS and CSRS fields that produced the left and right sidebands, and (d) for each sideband, the line shape changes from positive Lorentzian to dispersive to negative Lorentzian, then to negative dispersive and back to positive Lorentzian with the period of the bending vibration, and it is correlated with the momentum of the wave packet prepared on the ground-state surface by the impulsive pump along the sideband normal coordinate.     

Picosecond time-resolved multiplex CARS spectroscopy using optical Kerr gating

We have developed a new spectroscopic system for picosecond time-resolved coherent anti-Stokes Raman scattering (CARS) measurements. Using the optical Kerr gating method in conjunction with a nanosecond laser-based CARS system, a time resolution of 1 ps has been achieved. All-trans retinal in 1-butanol has been measured. The observed time-resolved CARS spectra show changes in the 0–10 ps time range, which are ascribed to the photoisomerization dynamics of all-trans retinal in solution.     

Selective excitation of molecular modes in a mixture by optimal control of electronically nonresonant femtosecond four-wave mixing spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) gives access to ultrafast molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this spectroscopy. However, it can be demonstrated that by shaping the femtosecond pulses a selective excitation of specific vibrational modes is possible. We demonstrate that using a feedback-controlled optimization technique, molecule-specific CARS spectra can be obtained from a mixture of different substances. A careful analysis of the experimental results points to a nontrivial control of the vibrational mode dynamics in the electronic ground state of the molecules as underlying mechanism.     

甲醇-水二元混合物中Co(bpb)与叠氮离子反应的动力学研究

Co(bpb) [bpbH2 is N,N'-o-phenylenebis(pyridine-2-carboxamide), C18H12N4O2] complex has active axial sites like a porphyrin complex. We studied the coordination of azide ion (N-3) to Co(bpb) in binary methanol-water mixtures by spectrophotometric method at the temperature range of 283-303 K. From the temperature dependence of the rate constant, activation parameters (Ea, △H#, △S#, and △G#) were obtained. An isokinetic temperature at about 302 K was observed at which the formation rate of Co(bpb)-N-3 was more or less independent of the solvent composition. The resulting △H against T△S plot showed a good linear correlation, indicating the existence of enthalpy-entropy compensation in azide complexation process. Under optimum conditions and based on the absorbance of Co(bpb)-N-3 produced through complex formation, a spectrophotometric method for the determination of N-3 in solution was developed.Alinear relationship between the absorbance and N-3 concentration was obtained in the range of (0.85-5.00)×10-4 mol·L-1 (3.6-21.0 μg·mL-1). The detection limit was 2.5×10-5 mol·L-1 (1.0 μg·mL-1). The proposed method was applied to the determination of N-3 anion in real water samples.     

Transient vibronic structure in ultrafast fluorescence spectra of photoactive yellow protein

The ultrafast photo-induced dynamics of wild-type photoactive yellow protein and its site-directed mutant of E46Q in aqueous solution was studied at room temperature by femtosecond fluorescence spectroscopy using the optical Kerr-gate method. The vibronic structure appears, depending on the excitation photon energy, in the time-resolved fluorescence spectra just after photoexcitation, which winds with time and disappears on a time scale of sub-picoseconds. This result indicates that the wavepacket is localized in the electronic excited state followed by dumped oscillations and broadening, and also that the initial condition of the wavepacket prepared depending on the excitation photon energy affects much the following ultrafast dynamics in the electronic excited state.     

Microkinetics of H2S Removal by Zinc Oxide in the Presence of Moist Gas Atmosphere

The microkinetics os H2S removeal by ZnO desulfurization in H2O-CO2-N2,H2O-CO-N2 and H2O-O2-N2 gas mixtures was studied by thermogravimetric andlysis.Experiments were carried out with 100-120 mesh ZnO powder at temperatures from 473K to 563K.The results show that the kinetic behaviors of desulfurization could all be described by an improved shrinking-core model.The activation energies of the reaction and the diffusion in different gas atmospheres were estimated.     

CH(A^2Δ)自由基被醇类分子猝灭动力学的温度效应研究

用266nm激光光解CHBr3产生CH自由基, 利用精密控温仪控制反应温度, 测定CH(A→X)荧光的时间分辨信号, 测量了290K至653K范围内CH(A)被乙醇、丙醇、丁醇猝灭的速率常数, 利用修正的碰撞配合物模型, 定性解释了在多极吸引势与活化势垒的双重影响下, 猝灭截面与温度间的关系。     

Femtosecond dynamics of cyclopropenylidene, c-C3H2

The photophysics of the B (1)B(1) state of isolated cyclopropenylidene, c-C(3)H(2), has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C(3)HCl. In the photoelectron spectrum of c-C(3)H(2) resonances were observed which can be assigned to members of a Rydberg d-series.     

Molecular distribution at the interface in an aqueous triethylamine solution. <Superscript>1</Superscript>H NMR

The ¹H NMR spectra in a binary aqueous triethylamine solution are recorded with a lower critical point of the liquid–liquid phase transition. It is found that, above the critical temperature the ¹H NMR spectra of water and triethylamine molecules in the phase with a predominant content of triethylamine molecules are characterized by an inhomogeneous broadening. It can be supposed that the found broadening is due to the features of the molecular distribution at the interface.