乙酰乙酸乙酯在重水和环己烷中的C=O和C=C伸缩振动模式的振动衰减动力学

作为典型的β-二羰基化合物和α,β-烯酮类化合物, 乙酰乙酸乙酯在溶液中以多结构存在. 在本文中, 我们利用飞秒中红外泵浦探测光谱技术, 研究了该化合物在重水和环己烷溶液中不同互变异构体的出现在波长6 μm(频率范围1600～1800 cm^-1)区域的C=O和C=C伸缩振动的振动动力学; 并结合稳态红外实验和量子化学计算, 分析了这些吸收峰的线型特征. 结果表明: 在重水中, 乙酰乙酸乙酯以酮式存在; 而在环己烷中以烯醇式和两种酮式共存. 分析稳态红外光谱可以看到, 烯醇式结构刚性, 其红外光谱线型主要表现为均匀增宽; 而酮式的线型则兼具均匀增宽和非均匀增宽. 而且, 即使在同一种溶剂中, 酮式和烯醇式的表观红外光谱线型也有不同. 通过泵浦探测实验获得了C=O和C=C伸缩振动衰减动力学和各向异性动力学. 重水中酮式的C=O的振动能量弛豫过程比其在环己烷中要快, 这可归因于乙酰乙酸乙酯与溶剂发生的分子间氢键作用. 此外, 烯醇式的C=O伸缩振动和一些振动模式(如COH面内弯曲)之间存在费米共振, 直接影响其快速衰减过程, 这也是造成其振动衰减动力学不同于酮式的原因. 各向异性动力学过程表明, 乙酰乙酸乙酯在重水中的转动速度比其在环己烷中要慢一些, 与它们不同的溶剂化情况有关. 此外, 各向异性动力学过程表现出量子拍频现象, 在酮式中尤为明显, 意味着相关振动模式存在相干激发.     

寡聚酰胺PyPyPybDp与DNA相互作用的荧光动力学

通过稳态吸收光谱、荧光光谱和时间分辨荧光光谱对寡聚酰胺分子PyPyPybDp(简称PPP)的光物理性质进行了详细研究. 发现PPP的激发态性质受溶剂环境影响较大, 在TKMC缓冲液中, PPP有较弱的荧光, 其荧光寿命为16 ps; 随着溶剂极性逐渐降低, 荧光光谱蓝移, 荧光强度增加, 相应荧光寿命增长. 通过对PPP与DNA双螺旋分子相互作用的荧光动力学研究表明, PPP与DNA相互作用后, 荧光强度增强, 荧光寿命从16 ps增加到32 ps, 证实了存在PPP与双螺旋DNA的结合相互作用.     

寡聚酰胺PyPyPyβDp与DNA相互作用的荧光动力学

通过稳态吸收光谱、荧光光谱和时间分辨荧光光谱对寡聚酰胺分子PyPyPy(Dp(简称PPP)的光物理性质进行了详细研究. 发现PPP的激发态性质受溶剂环境影响较大, 在TKMC缓冲液中, PPP有较弱的荧光, 其荧光寿命为16 ps; 随着溶剂极性逐渐降低, 荧光光谱蓝移, 荧光强度增加, 相应荧光寿命增长. 通过对PPP与DNA双螺旋分子相互作用的荧光动力学研究表明, PPP与DNA相互作用后, 荧光强度增强, 荧光寿命从16 ps增加到32 ps, 证实了存在PPP与双螺旋DNA的结合相互作用.     

担载于ZrO2上的Co2(CO)6(PBu3)2络合物及其分散型Co催化剂的研究

采用红外光谱、紫外漫反射光谱和程序升温分解技术研究了担载于ZrO_2和Zr(OH)_4上的Co_2(CO)_6(PBu_3)_2络合物在真空和空气中的脱羰基作用、结构变化过程及由此制得的分散型Co催化剂上Co的吸附态。结果表明,该络合物经担载后其羰基主频带均随载体的灼烧温度的增高而向低波数位移。表征Co—Co键电子跃迁和Co→CO电荷转移性质的紫外光谱特征带变化不大。担载络合物于真空加热时,随升温而逐渐脱去羰基,同时部分端羰基转变为桥羰基,完全脱羰基后可变为具有吸附CO能力的分散型Co金属催化剂。吸附的CO以线式存在。当样品暴露于空气时,CO吸附中心被破坏而不再出现吸附的CO振动频带。根据实验结果提出了在ZrO_2和Zr(OH)_4上的络合物的结构模型,并讨论了它们的分解机理,以及CO吸附在脱羰基后的分散型Co催化剂上的红外光谱。     

丙烯酰氯分子的气相光解动力学

利用时间分辨傅立叶变换红外(TR-FTIR)发射光谱研究了气相中CH2=CHCOCl分子的光解动力学.观测到振动激发的光解碎片分子CO(ν≤5),HCl(ν≤6),C2H2和相应的两个光解离通道:C-Cl键断裂和HCl消除通道.通过分析转动分辨的红外发射光谱得到CO和HCl的初始振转能量态分布,由此提出CH2=CHCOCl的气相光解机理并阐明了内转换等非绝热过程在影响反应途径中的关键作用.     

邻二氯苯激发态动力学

利用飞秒分辨的激光泵浦-探测技术结合飞行时间质谱和光电子速度成像方法研究了邻二氯苯第一电子单重激发态(S₁)的超快动力学.邻二氯苯的S₁态振动基态寿命为(651 ± 10) ps,对应于S₁振动基态向三重态的系间窜越过程.邻二氯苯S₁的高振动激发9a₂18a₂对应两个衰减通道,其中寿命为(458 ± 12) fs的超快过程对应于由处于振动激发的S₁向高振动激发的基态(S₀)发生的内转换过程,而寿命为(90 ± 10) ps过程则对应由S₁态向三重态(T₁)的系间窜越过程,电离产生的光电子能谱中长寿命的谱峰可能与系间窜越过程有关. S₁态高振动态的旋轨耦合程度比低振动态的更强,导致系间窜越过程更快.     

乙二醇的分子间氢键结构动力学的飞秒非线性红外光谱

利用稳态线性红外光谱和飞秒泵浦-探测红外光谱技术, 研究了在乙腈(MeCN)、丙酮(AC)、四氢呋喃(THF)和二甲基亚砜(DMSO)溶剂中乙二醇(EG)的结构和羟基(―OH)伸缩振动动力学. 结果表明, 乙二醇的―OH伸缩振动的频率位置、峰宽以及振动弛豫动力学都表现出强烈的溶剂依赖性. 乙二醇溶液中至少存在两种形式的分子间氢键, 一种是溶质-溶剂团簇的分子间氢键, 另一种是溶质-溶质团簇的分子间氢键. 量子化学计算预测的―OH伸缩振动频率的溶剂依赖性与我们的红外光谱实验观测结果一致. 进一步, 我们发现在乙腈中参与形成溶质-溶剂团簇氢键的乙二醇―OH伸缩振动具有最慢的弛豫动力学, 丙酮和四氢呋喃次之, 而最快的弛豫动力学过程发生在二甲基亚砜中. 在每一溶剂条件下, 乙二醇/乙二醇溶质团簇中―OH伸缩振动弛豫都更快一些. 本文结果有助于认识在溶质-溶质、溶质-溶剂分子团簇共存的体系中不同分子间氢键的结构动力学特性.     

CH_2(~3B_1)自由基与O_2的反应

用时间分辨宫里叶红外发射谱仪（TR-FTIRS），研究了自由基与O2反应的通道及产物的振动态布居．基电子态自由基由351nm紫外激光光解CH2CO生成．观测到振动激发态反应产物CO（v　10）、CO2（v3　7）、OH（H2O）和H2CO的红外发射，证实存在生成H2CO的通道．由光谱拟合得到不同时刻CO（v）和CO2（v2）的相对振动布居，发现v＝4能级的布居数相对于v3　3能级有明显反转．     

含C16长碳链1，2－邻二萘醌－2－肟钌（Ⅱ）配合物的合成

通过三种构型的1，2－邻二萘醌－2－肟（2－nqo)钌（Ⅱ）羰基配合物trans, cis－（Ru(2-nqo)2(CO)2](1){(trans-NO,cis-O},cis-,trans-[Ru(2-nqo)2(CO)2] (2){cis-NO,trans-O}及cis,-cis-[Ru(2-nqo)2(CO)2](3){(cis-NO,cis-O)}的去羰 基取代反应，合成了含C16长碳链2-nqo钌（Ⅱ）配合物trans-,cis-[Ru(2-nqo)2 (CO)(spy)](4),cis-,trans-(Ru(2-nqo)2(CO)(spy)(5),cis-,cis-[Ru(2-nqo)2 (CO)(spy)](6)及trans-,trans-(Ru(2-nqo)2(spy)2](7){(trans-NO,trans-O)}。 对其进行了红外、紫外－可见质谱及核磁人振测试，并利用^1H-^1H偶合二维核磁 技术对核磁共振峰进行了指认。     

担载的(π-C_5H_5)_2Fe_2(CO)_4及C_(10)H_(16)N[FeCo_3(CO)_(12)]络合物的表面表征

本文采用红外光谱、紫外漫反射光谱、穆斯堡尔谱和程序升温分解等方法研究了担载的(π—C_5H_5)_2Fe_2(CO)_4(Ⅰ)及C_(10)H_(15)N[FeCo_3(CO)_(12)](Ⅱ)络合物的表面模型及脱羰基过程。实验结果表明,络合物(Ⅰ)担载于Al_2O_3上时,其端羰基的红外振频带向高波数位移,而桥羰基的振频带却向低波数方向位移。紫外光谱表明,担载后络合物的结构没发生明显变化,络合物中的羰基在真空中随温度的升高逐渐脱去。络合物(Ⅰ)担载于ZrO_2上时其性质与以Al_2O_3为载体时相似,但红外振频带位移较小。这两种表面络合物脱羰基后均以Fe~(+++)的的型式存在于载体表面上。担载于Al_2O_3上的表面络合物(Ⅱ),在真空中脱羰基时,端羰基比桥羰基易于脱去,且前者可部分转化为后者。在CO气氛中脱羰基时,端羰基与桥羰基同时脱去,脱羰基后的样品以Fe~(+++)及Co~(++)的型式存在于Al_3O_3表面上。根据实验结果提出了担载络合物可能的结构模型,并讨论了表面络合物的分解机理。     

Discrete variable approaches to tetratomic molecules: part II: application to H2O2 and H2CO

We have carried out large-scale calculations for accurate vibrational energy levels of formaldehyde and hydrogen peroxide. The discrete variable representations of the radial and angular coordinates are employed together with the contraction scheme resulting from several diagonalization/truncation steps. The global potential energy surface due to Carter et al. [J. Mol. Spectrosc. 90 (1997) 729] is used for H2CO and due to Koput et al. [J. Phys. Chem. A 102 (1998) 6325] for H2O2. For both molecules, the calculated vibrational energy levels are characterized by combining vibrationally averaged geometries and expectation values of rotational constants with several adiabatic projection schemes for automatic quantum number assignments. The energy levels of H2CO involving the excited v2 and v3 vibrations appear as resonances beyond the zero-order picture consisting of uncoupled 3D stretching and 2D bending modes. The torsional energy levels of H2O2 are studied in great detail and different energy patterns occurring below and above the cis barrier are discussed. Our full dimensional calculations for H2O2 have shown that the OH triad levels, 2vOH, are symmetry adapted local mode states.     

Solvation-driven excited-state dynamics of [Re(4-Et-Pyridine)(CO)3(2,2'-bipyridine)]+ in imidazolium ionic liquids. A time-resolved infrared and phosphorescence study

Excited-state dynamics of [Re(Etpy)(CO)3(bpy)]+ was studied in three imidazolium ionic liquids by time-resolved IR and emission spectroscopy on the picosecond to nanosecond time scale. Low-lying excited states were characterized by TD-DFT calculations, which also provided molecular dipole moment vectors in the relevant electronic states. TRIR spectra in ionic liquids show initial populations of two excited states: predominantly bpy-localized 3IL and 3MLCT, characterized by nu(CO) bands shifted to lower and higher frequencies, respectively, relative to the ground state. Internal conversion of 3IL to the lowest triplet 3MLCT occurred on a time scale commensurate with solvent relaxation. The nu(CO) IR bands of the 3MLCT state undergo a dynamic shift to higher wavenumbers during relaxation. Its three-exponential kinetics were determined and attributed to vibrational cooling (units of picoseconds), energy dissipation to the bulk solvent (tens of picoseconds), and solvent relaxation, the lifetime of which increases with increasing viscosity: [EMIM]BF4 (330 ps) < [BMIM]BF4 (470 ps) < [BMIM]PF6 (1570 ps). Time-resolved phosphorescence spectra in [BMIM]PF6 show a approximately 2 ns drop in intensity due to the 3IL --> 3MLCT conversion and a dynamic Stokes shift to lower energies with a lifetime decreasing from 1.8 ns at 21 degrees C to 1.1 ns at 37 degrees C, due to decreasing viscosity of the ionic liquid. It is proposed that solvent relaxation predominantly involves collective translational motions of ions. It drives the 3IL --> 3MLCT conversion, increases charge reorganization in the lowest excited-state 3MLCT, and affects vibrational anharmonic coupling, which together cause the dynamic shift of excited-state IR bands. TRIR spectroscopy of carbonyl-diimine complexes emerges as a new way to investigate various aspects of solvation dynamics, while the use of slowly relaxing ionic liquids offers new insight into the photophysics of Re(I) carbonyl polypyridyls.     

Vibrationally quantum-state-specific dynamics of the reactions of CN radicals with organic molecules in solution

The dynamics of reactions of CN radicals with cyclohexane, d(12)-cyclohexane, and tetramethylsilane have been studied in solutions of chloroform, dichloromethane, and the deuterated variants of these solvents using ultraviolet photolysis of ICN to initiate a reaction. The H(D)-atom abstraction reactions produce HCN (DCN) that is probed in absorption with sub-picosecond time resolution using ～500 cm(-1) bandwidth infrared (IR) pulses in the spectral regions corresponding to C-H (or C-D) and C≡N stretching mode fundamental and hot bands. Equivalent IR spectra were obtained for the reactions of CN radicals with the pure solvents. In all cases, the reaction products are formed at early times with a strong propensity for vibrational excitation of the C-H (or C-D) stretching (v(3)) and H-C-N (D-C-N) bending (v(2)) modes, and for DCN products there is also evidence of vibrational excitation of the v(1) mode, which involves stretching of the C≡N bond. The vibrationally excited products relax to the ground vibrational level of HCN (DCN) with time constants of ～130-270 ps (depending on molecule and solvent), and the majority of the HCN (DCN) in this ground level is formed by vibrational relaxation, instead of directly from the chemical reaction. The time-dependence of reactive production of HCN (DCN) and vibrational relaxation is analysed using a vibrationally quantum-state specific kinetic model. The experimental outcomes are indicative of dynamics of exothermic reactions over an energy surface with an early transition state. Although the presence of the chlorinated solvent may reduce the extent of vibrational excitation of the nascent products, the early-time chemical reaction dynamics in these liquid solvents are deduced to be very similar to those for isolated collisions in the gas phase. The transient IR spectra show additional spectroscopic absorption features centered at 2037 cm(-1) and 2065 cm(-1) (in CHCl(3)) that are assigned, respectively, to CN-solvent complexes and recombination of I atoms with CN radicals to form INC molecules. These products build up rapidly, with respective time constants of 8-26 and 11-22 ps. A further, slower rise in the INC absorption signal (with time constant >500 ps) is attributed to diffusive recombination after escape from the initial solvent cage and accounts for more than 2/3 of the observed INC.     

Dual-frequency 2D IR on interaction of weak and strong IR modes

Dual-frequency 2D IR heterodyne photon-echo spectroscopy of C[triple bond]N and C=O stretching vibrational modes in 2-cyanocoumarin is reported. We have shown that the interaction among these modes provides convenient and useful structural constraints for molecules. Implementation of two pulse sequences, 4, 4, and 6 microm and 6, 6, and 4 microm, allowed the clear determination of contributions caused by vibrational relaxation. Positive correlation between C[triple bond]N and C=O frequency distributions was observed in 2-cyanocoumarin. Because C[triple bond]N modes are highly localized and have frequencies in a spectral region with minimal water absorption, the C[triple bond]N/C=O interactions have a strong potential for use as structural reporters in proteins. In addition to CN/CO peaks, the cross-peaks responsible for the C[triple bond]N/C=C interaction are also observed in the 2D IR spectra, where C=C is a coumarin ring stretching mode. We have demonstrated that 2D IR spectroscopy can utilize interactions of strong IR modes with weak local modes as structural reporters.     

Vibrational relaxation of CH3I in the gas phase and in solution

Transient electronic absorption measurements reveal the vibrational relaxation dynamics of CH(3)I following excitation of the C-H stretch overtone in the gas phase and in liquid solutions. The isolated molecule relaxes through two stages of intramolecular vibrational relaxation (IVR), a fast component that occurs in a few picoseconds and a slow component that takes place in about 400 ps. In contrast, a single 5-7 ps component of IVR precedes intermolecular energy transfer (IET) to the solvent, which dissipates energy from the molecule in 50 ps, 44 ps, and 16 ps for 1 M solutions of CH(3)I in CCl(4), CDCl(3), and (CD(3))(2)CO, respectively. The vibrational state structure suggests a model for the relaxation dynamics in which a fast component of IVR populates the states that are most strongly coupled to the initially excited C-H stretch overtone, regardless of the environment, and the remaining, weakly coupled states result in a secondary relaxation only in the absence of IET.     

Vibrational dynamics of acetate in D2O studied by infrared pump-probe spectroscopy

Solute-solvent interactions between acetate and D(2)O were investigated by vibrational spectroscopic methods. The vibrational dynamics of the COO asymmetric stretching mode in D(2)O was observed by time-resolved infrared (IR) pump-probe spectroscopy. The pump-probe signal contained both decay and oscillatory components. The time dependence of the decay component could be explained by a double exponential function with time constants of 200 fs and 2.6 ps, which are the same for both the COO asymmetric and symmetric stretching modes. The Fourier spectrum of the oscillatory component contained a band around 80 cm(-1), which suggests that the COO asymmetric stretching mode couples to a low-frequency vibrational mode with a wavenumber of 80 cm(-1). Based on quantum chemistry calculations, we propose that a bridged complex comprising an acetate ion and one D(2)O molecule, in which the two oxygen atoms in the acetate anion form hydrogen bonds with the two deuterium atoms in D(2)O, is the most stable structure. The 80 cm(-1) low-frequency mode was assigned to the asymmetric stretching vibration of the hydrogen bond in the bridged complex.     

Vibrational coherence transfer characterized with Fourier-transform 2D IR spectroscopy

Two-dimensional infrared (2D IR) spectroscopy of the symmetric and asymmetric C[Triple Bond]O stretching vibrations of Rh(CO)(2)acac in hexane has been used to investigate vibrational coherence transfer, dephasing, and population relaxation in a multilevel vibrational system. The transfer of coherence between close-lying vibrational frequencies results in extra relaxation-induced peaks in the 2D IR spectrum, whose amplitude depends on the coherence transfer rate. Coherence transfer arises from the mutual interaction of the bright CO stretches with dark states, which in this case reflects the mutual d-pi(*) back bonding of the Rh center to both the terminal carbonyls and the acetylacenonate ligand. For 2D IR relaxation experiments with variable waiting times, coherent dynamics lead to the modulation of peak amplitudes, while incoherent population relaxation and exchange results in the growth of the relaxation-induced peaks. We have modeled the data by propagating the density matrix with the Redfield equation, incorporating all vibrational relaxation processes during all three experimental time periods and including excitation reorientation effects arising from relaxation. Coherence and population transfer time scales from the symmetric to the asymmetric stretch were found to be 350 fs and 3 ps, respectively. We also discuss a diagrammatic approach to incorporating all vibrational relaxation processes into the nonlinear response function, and show how coherence transfer influences the analysis of structural variables from 2D IR spectroscopy.     

The role of CN and CO ligands in the vibrational relaxation dynamics of model compounds of the [FeFe]-hydrogenase enzyme

The vibrational dynamics of (μ-propanedithiolate)Fe(2)(CO)(4)(CN)(2)(2-), a model compound of the active site of the [FeFe]-hydrogenase enzyme, have been examined via ultrafast 2D-IR spectroscopy. The results indicate that the vibrational coupling between the stretching modes of the CO and CN ligands is small and restricted to certain modes but the slow growth of off-diagonal peaks is assigned to population transfer processes occurring between these modes on timescales of 30-40 ps. Analysis of the dynamics in concert with anharmonic density functional theory simulations shows that the presence of CN ligands alters the vibrational relaxation dynamics of the CO modes in comparison to all-carbonyl model systems and suggests that the presence of these ligands in the enzyme may be an important feature in terms of directing the vibrational relaxation mechanism.     

Infrared and molecular-dynamics studies of the rotational dynamics of water highly diluted in supercritical CO2

Far-infrared (FIR) and mid-infrared (MIR) profiles of D2O infinitely dilute in supercritical CO2 have been studied using molecular-dynamics simulations. For this purpose, we have proposed an intermolecular potential model taking implicitly into account electron donor-acceptor (EDA) interactions between water and CO2 evaluated from ab initio calculations of the intermolecular potential-energy surface (IPS). Interaction-induced dipole mechanisms have been also taken into account in addition to the water permanent dipole to evaluate the simulated FIR profiles of water and CO2 polarizable molecules. They were found to play a minor role in the genesis of the FIR profiles of water/CO2 under supercritical conditions. The analysis of the reorientational dynamics of D2O shows that the rotational dynamics of water is weakly anisotropic due to the EDA interactions which affect more specifically the reorientational motions of the C2 symmetry axis of solute. These results have been used to assess the contribution of the vibrational relaxation in the experimental mid-infrared profiles associated with the nu1 symmetric and nu3 antisymmetric stretching and nu2 bending modes of D2O. It was found that the rotational dynamics mainly contribute to the broadening of the infrared (IR) profiles. Nevertheless, the vibrational processes play a role in the frequency shifts of the band centers and the relative intensity enhancements of the nu1 and nu3 modes of D2O. In particular, the EDA interactions between water and CO2 lead to the appearance of a well-defined IR band of the nu1 mode of D2O. Finally, a comparison with another model taking only into account dipole-quadrupole electrostatic interactions between water and CO2 molecules clearly reveals that EDA interactions have to be considered to reproduce both MIR and FIR measurements. From this point of view CO2 can be classified on a hydrophilic solvent scale based upon the solubility criterion as an intermediate solvent between "inert" xenon and carbon tetrachloride.     

Theoretical Study of the Solvent Effect on the Electronic and Vibrational Properties of [CpFe(CO)<Subscript>2</Subscript>(NCS)] and [CpFe(CO)<Subscript>2</Subscript>(SCN)] Linkage Isomers

The present study illustrates the stability of [CpFe(CO)₂(NCS)] and [CpFe(CO)₂(SCN)] linkage isomers by the use of MPW1PW91 quantum method in the gas and solution phases. Our results reveal that the [CpFe(CO)₂(NCS)] isomer is more stable than the [CpFe(CO)₂(SCN)] isomer. Based on the polarizable continuum model, the effect of the solvent polarity on the stability, structural parameters, frontier orbital energies, and vibrational modes of carbonyl ligands (ν_CO) of these linkage complexes is explored. The molecular orbital analysis suggests that the major contributions to HOMO and LUMO arise from the ambidentate ligand and Fe in two isomers, respectively. In addition, the bonding interaction between the CpFe(CO)₂ fragment and the ambidentate ligand is studied by means of the energy decomposition analysis. The back-bonding effect in Fe–CO bonds is revealed in the calculation of the quadrupole polarization of the carbon atom by the QTAIM analysis. The character of Fe–N and Fe–S bonds in these complexes is analyzed by the natural bond orbital analysis.