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1.
硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。 相似文献
2.
The D 1-D 0 electronic spectrum of jet-cooled cyanocyclopentadienyl (C 5H 4CN) radical, produced by excimer laser photolysis of 1,3-cyclopentadiene-1-carbonitrile (C 5H 5CN), was measured by laser-induced fluorescence (LIF). The LIF spectrum was identical to that of radicals produced by photolysis of phenyl isocyanate and o-chloroaniline, which had been assigned to phenyl nitrene. This result shows that the nascent radical product in the photolysis of o-chloroaniline and phenyl isocyanate is isomerized to C 5H 5CN and the final product of C 5H 4CN radical is derived via the second photolysis. The rotational contour of the 0-0 band of the C 54CN radical, at 27143 cm −1 (368.3 nm), is also presented. The electronic transition is A-type and π electron transition, and the symmetry of both the ground and excited electronic state is 2B 1 (of the C 2v point group). 相似文献
3.
用B 3LYP/6-311G(d,p)密度泛函方法对B 2H 5+阳离子和B 2H 5·自由基的几何异构体的空间构型进行了优化,并在此基础上用QCISD(T)/6-311++G(3df,2p)偶合簇法进行了单点能计算和零点能校正.结果表明,B 2H 5+单态有2种稳定的几何构型(D 3h,C 1),其中C 1构型是新发现的.B 2H 5+三重态阳离子除已知C s构型外,又发现两种稳定构型(C 1).对于B 2H 5·自由基体系,共有4种异构体(包括两种新发现的构型C s),其中,具有单桥结构的C 2v最稳定.用二级多体微扰理论和密度泛函方法对前人所认为稳定的B 2H 5+单态的C 2v构型进行了全优化,结果发现该构型始终具有一个虚频,不是稳定构型.对B 2H 5-阴离子体系的单态和三重态进行的全优化,理论上得出单态时具有C 2v和C s两种稳定构型,而三重态只有C 2v一种稳定构型. 相似文献
4.
Small carbon clusters C, C 2 and C 3 metallized with beryllium were studied by first principles within the hybrid density functional approach with generalized gradient correction. Cluster isomer structures for the ground state and several excited states where systematically calculated for C xBe y with x = 1–3 and y = 1–4 including the vibrational analysis of all states. Ionization potentials and electron affinities are calculated for the ground state cluster isomers. The thermal stability of the ground state isomers was verified within the harmonic approximation of the Helmholtz free energy up to temperatures of about 1000 K. Within the family of clusters studied, C 2Be 3 undergoes a solid-like structural transition at about 260 K changing from a planar structure at low temperatures to a linear isomer at high temperatures. 相似文献
5.
The oxidative dehydrogenation of ethane over NiO-loaded MgO with high surface area was carried out using a fixed-bed flow reactor at 600 °C under atmospheric pressure. At 600 °C, the oxidative dehydrogenation of ethane (C2H6/O2 = 1) without dilution with an inert gas resulted in C2H6 conversion of 68.8% and a high C2H4 selectivity of 52.8%, which corresponds to a C2H4 yield of 36.3%. In addition, the catalytic activity did not decrease for at least 10 h. X-ray photoelectron spectra of the catalysts after the reaction exhibited that the initial valence state of Ni2+ (NiO) was maintained during the oxidative dehydrogenation of ethane. However, when NiO-loaded MgO was reduced with H2 prior to the reaction, C2H4 selectivity decreased to nearly zero and high CO and H2 selectivities were observed with the C2H6 conversion of 50 %, indicating that partial oxidation of C2H6 proceeded. Therefore, it seems important to keep Ni species as an oxide phase on the support, and for this purpose, use of the high surface area of MgO is essential. 相似文献
6.
1H NMR spectra of binuclear metallocene hydride complexes, (η 5 : η 5-C 10H 8)(C 5H 5) 2M 2(μ-H) 2 (M = Nb, 20°C and Ti, (−60 to +25°C), were studied. The Nb complex is diamagnetic and gives a high resolution spectrum. The coordination of bridging hydride H atoms provides Nb atoms with complete 18 electron configuration. In its ground state, the Ti complex is also diamagnetic (the spectrum at −60°C agrees to that) in spite of only 17 electron configuration of each Ti atom. However, the population of the excited triplet state in the case of the Ti complex is appreciable at temperatures higher than −30°C, the proton resonance lines being shifted downfield and significantly broadened as compared with the spectrum at −60°C. 相似文献
7.
应用密度泛函B 3LYP方法和从头算(abinitio)HF方法,在3-21G理论水平上,对具有C 2v,D 2d,D 3h和D 6h对称性的四种C 36异构体以及在保持D 2d,D 3h和D 6h对称性条件下形成的不同氢化物进行了量子化学计算,研究了它们在不同量子态时的分子几何构型和电子结构.结果表明,电子相关效应在C 36簇化合物的电子结构中起着重要作用.它们最稳定的结构是C 36的 3A 2u量子态D 6h异构体,而C 36的氢化物是在D 3h异构体的C 2位置等同碳原子上形成的 1A 1'量子态氢化物C 36H 12. 相似文献
8.
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A 2A″ state (C 2H 3 (A 2A″)) and examined possible pathways for nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C 2H 3 in the A 2A″ state were explored: (1) C 2H 3 (A 2A″) → C 2H 2 ( trans, 3A u) + H, (2) C 2H 3 (A 2A″) → C 2H 2 ( cis, 3A 2) + H, and (3) C 2H 3 (A 2A″) → H 2CC ( 3A 2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C 2H 3 (A 2A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C 2H 3 (A 2A ′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C 2v bridge structures in the 2B 2, 2A 2, 2B 1, and 2A 1 states along the pathways of the 1 2A ′ (X 2A ′), 1 2A″ (A 2A″), 2 2A″, and 2 2A ′ states of C 2H 3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C 2v ( 2A 2) structure and then 2A 2/ 2A 1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C 2v ( 2A 2) structure could not be accessed. 相似文献
9.
以三苯胺为单体, 无水三氯化铁为催化剂, 二甲醇缩甲醛为外交联剂, 通过机械球磨不同比例的三苯胺、 三氯化铁和二甲醇缩甲醛, 合成了PAF-106s(PAF-106a~PAF-106c, PAF: porous aromatic framework). 红外光谱、 元素分析、 X射线光电子能谱和固体核磁共振波谱等表征结果证明发生了聚合反应. 氮气吸附结果表明, 三苯胺、 三氯化铁和二甲醇缩甲醛的比例影响PAF-106s的多孔性能. 三氯化铁和三苯胺摩尔比从3∶1增加到12∶1时, PAF-106c的BET比表面积从PAF-106a的135 m 2/g增加到280 m 2/g. 引入二甲醇缩甲醛后, PAF- 106d~PAF-106g的BET比表面积随三氯化铁和二甲醇缩甲醛摩尔比的增加而逐渐降低. 在273和298 K下, 测试了PAF-106c的C2烃吸附性能, 并采用理想吸附溶液理论计算了C 2H 2/C 2H 4和C 2H 6/C 2H 4分离比. 相似文献
10.
The complex triplet potential energy surface of the C 2H 3N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C 2H 3 radical with N( 4S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C 2H 3+N( 4S), the first step is the attack of the N atom on the C atom having one H atom attached in C 2H 3 radical and form the intermediate C 2H 3N(1). The associated intermediate 1 can lead to product P 1 CH 2CN+H and P 2 3CH 2+ 3HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C 2H 3+N( 4S) reaction is the channel leading to P 1, which is preferred to that of P 2 due to the comparative lower energy barrier. The formation of P 3 3C 2H 2+ 3NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively. 相似文献
11.
运用密度泛函理论研究了(1,3,5-C3P3H3)M和(1,3,5-C3P3H3)2M (M=Ti,V,Cr)的结构、键合能以及芳香性.结果表明:低自旋的(1,3,5-C3P3H3)M和(1,3,5-C3P3H3)2M基态结构分别具有C3v和D3h对称性.金属与配体间为共价作用,二者之间存在σ、π和σ三种成键方式.V的三明治配合物的解离方式与Ti和Cr的三明治配合物不同,前者为分步解离,后两者则为一步解离.其中(1,3,5-C3P3H3)2Cr(D3h)的第一解离能最大,配合物最稳定.这些三明治和半三明治配合物都具有中心芳香性、内芳香性和外芳香性,且中心芳香性均大于自由配体(1,3,5-C3P3H3)的中心芳香性,芳香性主要贡献来源于π键和金属原子的孤对电子.内芳香性按照Ti、V、Cr的顺序依次增大,且内芳香性明显要大于外芳香性.高自旋的半三明治(1,3,5-C3P3H3)Ti(C3,5A1)与单重态(1,3,5-C3P3H3)Ti (C3v,1A1)相比,配体的变形性增大,稳定性增加,且C平面中心芳香性和内芳香性均增大,但P平面的中心芳香性却降低. 相似文献
12.
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9a 218a 2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. 相似文献
13.
采用[CCSD(T)]-F12方法和aug-cc-pVTZ基组,同时引入中心键函数(3 s3 p2 d1 f1 g)构建了Kr-C 2H 2体系的高精度四维势能面.在构建势能面时考虑了分子间的振动方式及C 2H 2单体内的 ν1对称伸缩和 ν3反对称伸缩振动.将计算得到的四维势能面在 Q1方向和 Q3方向分别做积分得到C 2H 2单体分别处于振动基态和( ν1, ν3)=(1,1)激发态的平均势能面.计算结果表明,这2个平均势能面均存在2个等价的T型全局极小值和2个等价线性极小值.全局极小值的几何构型位于 R=0.41 nm, θ=65.6°/114.4°,势阱深度为151.88 cm -1.对径向部分采用离散变量表象法(DVR),角度部分采用有限基组表象法(FBR),并结合Lanczos循环算法计算了Kr-C 2H 2的振转能级和束缚态.计算结果表明,复合物在( ν1, ν3)=(1,1)区域的带心位移为-1.48 cm -1,表现为红移,与实验值-1.38 cm -1很接近;计算得到的红外跃迁频率也与实验值相吻合,说明得到的从头算势能面具有高精度. 相似文献
14.
在常压下, 研究了添加气的种类(N 2, He, Ar, H 2, NH 3, CO和CO 2)对介质阻挡放电低碳烷烃(甲烷、 乙烷和丙烷)转化制低碳烯烃的影响. 结果表明, 以甲烷或乙烷为原料时, N 2, He, Ar和CO的引入有利于提高原料的转化率和总烯烃的选择性; 而CO 2, H 2和NH 3的引入对甲烷、 乙烷的转化率无明显影响, 但H 2和NH 3的引入会使总烯烃的选择性显著降低. 以丙烷为原料时, 所研究的添加气均可提高丙烷的转化率, 而只有CO的引入可提高总烯烃选择性. 综上所述, 80%(摩尔分数) CO添加量最有利于低碳烷烃转化成低碳烯烃, 对应的甲烷、 乙烷和丙烷的转化率分别提高了14.4%, 17.6%和42.8%, 总烯烃的选择性分别提高了19.9%, 25.0%和11.9%. 以CH 4为例, 通过对放电电流波形和等离子体区物种的发射光谱(OES)研究发现, 引入CO能显著增加等离子体的电子密度, 并且体系中出现激发态O *物种(777.5和844.7 nm), 这种O *物种能够促进C-H键的断裂, 有利于烯烃的生成. 因此, 等离子体区电子密度的增加和激发态O *物种的出现可能是CH 4-CO体系中CH 4有效转化的主要原因. 相似文献
15.
Ab initio study of the reactions of n-heptyl radicals(1-C 7H 15, 2-C 7H 15, 3-C 7H 15, and 4-C 7H 15) with methanol was conducted over the temperature range of 300-1500 K. Transition states for the reaction channels producing C 7H 15OH, CH 3, C 7H 15OCH 3, H, C 7H 16, CH 2OH and CH 3O were identified and the geometries of all stationary points were calculated at BB1K/MG3S level of theory. The potential barrier heights of the corresponding transition states were predicted by the CBS-QB3//BB1K and G4//BB1K methods, indicating that the eight H-abstraction channels are more kinetically favorable than the channels where OH transfers from CH 3OH to C 7H 15 and where the C 7H 15OCH 3+H products are given. The rate constants of H-abstraction channels were calculated with TST and TST/Eck. Both the forward and reverse rate constants have positive temperature dependence and the tunneling effect is only important at the temperature lower than 700 K. For the reactions of H-atom abstraction from methyl in CH 3OH by n-heptyl, a reverse and the corresponding forward rate constant are roughly equal. For the reactions of H-atom abstraction from OH in CH 3OH by n-heptyl, a reverse rate constant is larger by several orders of magnitude than the corresponding forward one. 相似文献
16.
Using velocity map ion imaging technique, the photodissociation of n-C 4H 9Br in the wavelength range 231–267 nm was studied. The results and our ab initio calculations indicated that the absorption of n-C 4H 9Br in the investigated region originated from the excitations to the lowest three repulsive states, as assigned as 1A″, 2A′ and 3A′ in C s symmetry. Dissociations occurred on the PES surfaces of the three states, terminating in C 4H 9+Br ( 2P 3/2) or C 4H 9 + Br * ( 2P 1/2) as two channels, and being impacted by an avoided crossing between the PES surfaces of the 2A′ and 3A′ states. The transition dipole to the 1A″ state was perpendicular to the symmetry plane, so perpendicular to the C–Br bond. The transitions to the 3A′ state was polarized parallel to the symmetry plane, and also parallel to the C–Br bond. While the transition dipole to the 2A′ state was in the symmetry plane, but formed an angle of about 53.1° with the C–Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways, for the photolysis of n-C 4H 9Br near 234 nm and 267 nm. 相似文献
17.
The photodissociation dynamics of the 3s Rydberg state of three ketones (CH 3CO–R, R=C 2H 5, C 3H 7, and iso-C 4H 9) and the ensuing dissociation of the nascent acetyl radical following 195 nm excitation were investigated by ultrafast photoionization spectroscopy. The 3s state the lifetimes of these ketones are similar (2.5–2.9 ps), though lifetimes of the acetyl radical range from 8.6 ps for CH 3CO–C 2H 5, 15 ps for CH 3CO–C 3H 7, to 23 ps for CH 3CO–( iso-C 4H 9), which suggests that for larger R more vibrational degrees of freedom compete for the excess energy so that less energy is partitioned into the internal energy of the acetyl radical. 相似文献
18.
LnCl 3 (Ln=Nd, Gd) reacts with C 5H 9C 5H 4Na (or K 2C 8H 8) in THF (C 5H 9C 5H 4 = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C 5H 9C 5H 4)LnCl 2(THF) n (orC 8H 8)LnCl 2(THF) n], which further reacts with K 2C 8H 8 (or C 5H 9C 5H 4Na) in THF to form the litle complexes. If Ln=Nd the complex (C 8H 8)Nd(C 5H 9C 5H 4)(THF) 2 (a) was obtained: when Ln=Gd the 1 : 1 complex [(C 8H 8)Gd(C %H 9)(THF)][(C 8H 8)Gd(C 5H 9H 4)(THF) 2] (b) was obtained in crystalline form. The crystal structure analysis shows that in (C8H8)Ln(C5H9C5H4)(THF)2 (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η5), cyclooctatetraenyl (η8) and two oxygen atoms from THF are coordinated to Nd3+ (or Gd3+) with coordination number 10. The centroid of the cyclopentadienyl ring (Cp′) in C5H9C5H4 group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd3+ (or Gd3+). In (C8H8)Gd(C5H9C5H4)(THF), the cyclopentyl-cyclopentadienyl (η5), cyclooctatetraenyl (η8) and one oxygen atom are coordinated to Gd3+ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd3+, which is almost in the plane (dev. -0.0144 Å). 相似文献
19.
A molecular thermodynamic model developed previously for fluids of chain-like molecules has been extended to correlate the pVT behavior of ionic liquids and the solubilities of gases such as CO 2, C 3H 6, C 3H 8, C 4H 10 in various ionic liquids. The relative deviation between the calculated molar volume and experimental data is less than 0.2%. It is shown that this equation of state can be used to correlate the solubility of CO 2 in ionic liquids with only one temperature-independent adjustable interaction parameter, and the accuracy of the correlation can be further improved using two temperature-independent adjustable parameters. The water content of ionic liquids has a large influence on the calculated results. For systems with water content lower than 0.1%, the average relative deviations of bubble point pressure are 3.14 and 4.90% using two parameters and one parameter, respectively. For systems containing C 3H 6, C 3H 8 and C 4H 10 two temperature dependent adjustable parameters are needed to obtain a good fit, and the corresponding deviation of the gas solubility is less than 2%, except for C 3H 8. 相似文献
20.
对2~6个环的多环芳烃的氢提取反应类进行了系统研究, 提取氢原子的不饱和自由基包括丙炔基自由基(C 3H 3)、 烯丙基自由基(C 3H 5)、 丁二烯基自由基(nC 4H 5, iC 4H 5)、 环戊二烯基自由基(C 5H 5)以及苯基自由基(C 6H 5). 采用M06-2X/cc-pVTZ方法得到了多环芳烃的电子结构信息, 利用过渡态理论并结合Eckart隧道校正, 计算了所有反应在500~2500 K范围内的反应速率常数.考察了多环芳烃的大小、 结构对反应速率常数的影响, 对比了不同氢提取自由基及不同氢提取反应类型的速率常数. 结果表明, 多环芳烃的大小对反应速率常数影响不大, 但是多环芳烃的环结构对反应速率常数影响较大. 将不同的氢提取反应类简化为发生在五元环上的C 5类和发生在六元环上的C 6类两类, 结果表明, C 6类的反应活性高于C 5类. 研究了nC 4H 5, iC 4H 5以及C 6H 5自由基与多环芳烃的氢提取反应, 它们的氢提取反应活性大小顺序为C 6H 5>nC 4H 5>iC 4H 5. 通过对每类典型反应的速率常数取平均值, 总结出相应类型的速率规则, 可用于构建多环芳烃和碳烟机理. 相似文献
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