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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 structures of alkali halide clusters Na nF n, Li nF n and Na nCl n, and their metal-excess clusters Na nF n−1+, Li nF n−1+ and Na nCl n−1+ were investigated by the ab initio molecular orbital method for cluster sizes from 1 to 14. The magic numbers for the neutral clusters Na nF n, Li nF n and Na nCl n are 4, 6, and 8. The most stable structure for these cluster sizes is a perfect crystallite for Na nF n and Na nCl n, and a double ring for Li nF n. The magic numbers for the metal-excess clusters are 5 and 8, which are near ideal cuboids with (100) facets. 相似文献
3.
复杂水盐体系存在稳态和介稳固液相平衡以及复杂的成盐规律。为了解固液平衡状态下液相的结构特征,本文采用拉曼光谱技术并结合高斯-洛伦兹去卷积分峰拟合程序对Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系及其二元和三元子体系中 ν1-SO 42-的离子缔合结构特征进行了分析。研究结果表明:SO 42-在Na 2SO 4-H 2O体系存在自由态SO 42-和SO 42-离子簇两种结构,在MgSO 4-H 2O, MgSO 4-MgCl 2-H 2O及Na +, Mg 2+//SO 42-, Cl -, H 2O等含镁体系中,还有Mg 2+-H 2O-SO 42-和Mg 2+-OSO 32-两种缔合结构。在二元和三元体系中 ν1-SO 42-的离子缔合结构以自由态SO 42-为主,随着SO 42-离子总浓度的变化,上述四种结构所占比例会发生规律性变化。Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系在NaCl减少及等温蒸发过程中,自由态SO 42-结构比例逐步降低, Mg 2+和SO 42-相结合形成Mg 2+-H 2O-SO 42-或Mg 2+-OSO 32-结构的机会增多,在复盐区还会形成SO 42-离子簇结构。由此判断溶液结构的适应性变化是导致介稳现象的重要原因。进一步的相关分析表明:SO 42-的浓度和耶涅克指数 J与 ν1-SO 42-峰的峰强度和峰面积存在正相关关系, Mg 2+浓度是影响 ν1-SO 42-峰中四种缔合结构的比例发生变化的主要因素。 相似文献
4.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
5.
Two novel types of transition-metal-containing liquid crystals, bis( p-n-koxydithiobenzoato)nickel(II) (abbreviated as (C nO-DTB) 2Ni), and ( p-n-alkoxydithiobenzoato)( p-n-alkoxyperthiobenzoato)nickel(II) (abbreviated as (C nO-DTB)(C nO-PTB)Ni), were synthesized. It was found that the (C nO-DTB) 2Ni complex for n = 8 has smectic H and C mesophases, and that the (C nO-DTB) 2Ni complexes for n = 4 and 8 easily transform into the corresponding monoperthio complexes, nO-PTB)Ni, by heating at temperatures between 230°C and 285°C. It was confirmed that the transformation originates from an intermolecular reaction between the (C nO-DTB) 2Ni complexes at high temperatures, and that the origin of the extra sulphurs in the resulting (C nO-DTB)(C nO-PTB)Ni complexes is the neighbouring (C nO-DTB) 2Ni complexes. Interestingly, each of the (C nO-DTB)(C nO-PTB)Ni complexes ( n = 4 and 8), has nematic mesophase and exhibits a unique double melting behaviour via the nematic phase, which is the first example in liquid crystals. The reversible transformation between the blue smectic rod-like (C nO-DTB) 2Ni complex and the red nematic Λ-like (C nO-DTB)(C nO-PTB)Ni complex is possible. 相似文献
6.
The thermodynamic data (Δ G0, Δ H0 and TΔ S0) of the solvation of tetraphenylarsonium-tetraphenylborate (Ph 4AsPh 4B) and its neutral parts, tetraphenylgermanium (Ph 4Ge) and tetraphenylmethane (Ph 4C) in methanol— N,N-dimethylformamide mixed solvents are discussed. The values of the free energy of transfer, ΔsMG0, are calculated from measurements of the solubilities of Ph4AsPh4B, Ph4Ge and Ph4C in the successive fractions of MeOH in DMF at three different temperatures (15, 25, 35°C). The values of ΔsMH0 and TΔsMS0 for the derivatives are calculated from ΔsMG0 values. The values of ΔsMG0, ΔsMH0 and TΔsMS0 of tetraphenylarsonium and tetraphenylborate ions have also been carefully calculated. The ratios of ΔsMG0 values (ΔsMG0 = ΔG0(+)/ΔG0(−)) were found to be greater than unity. Similarly, the ratios of ΔsMH0 and TΔsMS0 for the positive and negative ions were found to be greater than unity. 相似文献
7.
通过共沉淀法制得类球形锂离子电池正极材料LiNi 1/3Co 1/3Mn 1/3O 2,并用非水相共沉法对其进行CoAl 2O 4包覆得到LNCMO(x). 采用X射线衍射(XRD)、扫描电子显微术(SEM)和透射电子显微术(TEM)测试材料的结构和观察材料形貌. 结果表明,CoAl 2O 4在材料表面形成8 nm均匀包覆层,未改变主体材料的结构. 电化学性能测试表明,1%(by mass)CoAl 2O 4包覆量的LiNi1/3Co1/3Mn1/3O2材料(LNCMO(1))高充电电压(3.0 ~ 4.6 V,150 mA·g -1)100周期循环放电容量保持率为93.7%(无包覆LNCMO(0)保持率为74.4%);55 °C高温100周期循环容量保持率为77%(无包覆LNCMO(0)保持率17%). XRD和电感耦合等离子体原子发射光谱(ICP-AES)测试表明,CoAl 2O 4包覆的LNCMO(x)材料可有效地减缓材料中Mn离子在电解液的溶解,提高材料结构稳定性和热稳定性. 相似文献
8.
Closo-B nH n−2(CO) 2 ( n = 5–12), isolobal analogues of closo-C 2B n−2H n, have been investigated at the B3LYP/6-311+G **density functional level of theory. The most stable isomers of closo-B nH n−2(CO) 2 are similar to those of closo-C 2B n−2H n in geometric patterns apart from closo-B 6H 4(CO) 2, and closo-B nH n−2(CO) 2 is much less strained than closo-C 2B n−2H n. Energetic analysis identifies closo-B 6H 4(CO) 2, closo-B 12H 10(CO) 2 and closo-B 10H 8(CO) 2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B nH n−2(CO) 2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed. 相似文献
9.
A variety of terminal chain modifications ( Y) were made on the diacetylenes in which X=C nH 2n+1, C 12H 25O and F, and Y=CH 2CH(Me)C 2H 5, COCH 3, C≡CC 5H 11, C nF 2n+1C nH 2n+1 and CH=CHCO 2C 3H 7. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These were compared with those for the dialkyl analogues ( X=C mH 2m+1, Y=C nH 2n+1) and a series of 1- and 2-olefins ( Y=CH=CHC nH 2n+1 and CH 2CH=CHC nH 2n+1). The 1-olefin series showed wider range nematics than the dialkyl compounds, whereas the above modifications showed either narrow range nematic phases, no mesophase or higher melting temperatures. New transition temperature and enthalpy data are provided for some of the dialkyl and F-alkyl compounds previously reported, for comparisons. Preliminary birefringence data are also included along with the results of some heat and UV stability studies. 相似文献
10.
Mössbauer spectra of /pheophytinato a/ iron/III/ chloride [Fe/Pheo-a/Cl] and /pheophytinato b/ iron/III/ chloride [Fe/Pheo-b/Cl] have revealed that the central iron/III/ ion is in a high-spin state and axially coordinated by chloride ions in solid phase. Temperature-dependent asymmetry observed for the quadrupole splitting doublet of iron/III/ pheophytins, i.e., Fe/Pheo-a/Cl and Fe/Pheo-b/Cl, is interpreted on the basis of the zero-field splitting. The structural difference between iron/III/ pheophytins and iron/III/ porphyrins is reflected in the quadrupole splitting more than in the isomer shift. Magnetic behaviour of iron/III/ pheophytins near 4.2 K is very similar to that of iron/III/ porphyrins. 相似文献
11.
A series of Me nAg 0.3Mo 0.5P 0.3O y (Me=Cu, Zn, Mn, W, Ce, Pr, Nd) and Ag 0.3Mo 0.5P 0.3O x catalysts were prepared. The addition of Ce to Ag 0.3Mo 0.5P 0.3O x catalysts improved the catalytic performance in selective oxidation of propane to acrolein, and Ce 0.1Ag 0.3Mo 0.5P 0.3O x catalysts showed the highest acrolein selectivity (28.7%) and yield (4.4%). The physicochemical properties of Ag 0.3Mo 0.5P 0.3O x and Ce nAg 0.3Mo 0.5P 0.3O x ( n=0.1–0.5) catalysts have been comparatively characterized by BET, XRD, H 2-TPR, XPS, EPR and C 3H 8(C 3H 6)-TPD. Significant differences in physicochemical properties between Ag 0.3Mo 0.5P 0.3O x and Ce doped Ag 0.3Mo 0.5P 0.3O x catalysts have been observed, which is due to the formation of the redox cycle (Ce 3++Mo 6+Ce 4++Mo 5+) in the Ce nAg 0.3Mo 0.5P 0.3O y catalyst. Such effect modified the reducibility, the concentration of Mo 5+, the activation of propane and the transformation of possible intermediate propene to acroelin, which in return greatly influenced the catalytic performance of Ce doped Ag 0.3Mo 0.5P 0.3O x catalysts in selective oxidation of propane to acroelin. The proper addition of Ce to Ag 0.3Mo 0.5P 0.3O x catalyst improved the acrolein selectivity and yield. 相似文献
12.
Abstract— The rate constant k 5/ > for physical quenching of singlet oxygen O 2(δ 1;) by the sensitizer in dye-sensitized photooxygenations is determined in the case of chlorophylls a and b (7.3 times 10 8, 4.2 times 10 8 M -1 s -1 respectively), pheophytins a and b (7.4 times 10 7, 3.0 times 10 7 M -1 s _1 respectively), tetraphenylporphyrin (4.4 times 10 7 M -1 s _1), magnesium tetraphenylporphyrin (5.0 times 10 8 M -1 s _1), zinc tetraphenylporphyrin (1.5 times 10 8 M -1 s _l) and protoporphyrin IX-dimethylester (9.1 times 10 7 M -1 s _1) in benzene. These sensitizers show a linear correlation between log k sO , and their half-wave oxidation potentials and the value of the slope is similar to that observed for various compounds such as phenols. It is concluded that (i) the interaction between chlorophylls and related compounds with singlet oxygen may involve an exciplex as for phenols, and (ii) physical quenching may be envisaged as a spin-orbit-induced intersystem crossing within the exciplex. 相似文献
13.
锂硫电池的实际能量密度不高和多硫化物(LiPSs)的穿梭效应等问题严重影响了该电池的实际应用。本文通过将二维的Ti 3C 2T x Mxene纳米片与碳黑/硫(CB/S)材料进行混合,制备了Ti 3C 2T x-CB/S正极材料并将其涂覆在商业隔膜(PP)上,最终获得了Ti 3C 2T x-CB/S-PP一体式电极并用于锂硫电池。利用Ti 3C 2T x纳米片对CB/S进行修饰,不仅能提高活性物质硫的导电性,还能对扩散的LiPSs进行物理阻挡和化学吸附。而一体式电极的设计有利于提高电池的能量密度。恒流充放电测试结果表明,Ti 3C 2T x-CB/S-PP电极在0.1 C电流下的初始放电容量为1028.8 mAh·g -1,高于不含Ti 3C 2T x的CB/S-PP电极的896.8 mAh·g -1。Ti 3C 2T x-CB/S-PP电极还展示出了比基于传统铝箔集流体的Ti 3C 2T x-CB/S-Al电极更好的循环稳定性,前者在0.5 C下400圈长循环测试中的每圈衰减率为0.072%,而后者则为更高的0.10%。本文利用Ti 3C 2T x-CB/S构建一体式电极的策略为实现高性能和高能量密度的锂硫电池提供了新的研究方向。 相似文献
14.
采用分步浸渍法制备了系列Mg改性的Co/γ-Al_2O_3-TiO_2催化剂,通过X射线衍射(XRD)、紫外可见漫反射光谱(DR-UV-vis)、N_2吸附-脱附(BET)、X射线光电子能谱(XPS)和H_2程序升温还原(H_2-TPR)等技术对催化剂进行表征,并考察了其对丙烷燃烧的催化性能。结果表明,Co在原始γ-Al_2O_3-TiO_2载体和Mg改性MgO/γ-Al_2O_3-TiO_2载体上均以Co_3O_4的形式存在;Mg掺入后与Al_2O_3作用形成MgAl_2O_4尖晶石,改善了载体的织构性质,提升了Co_3O_4在催化剂载体表面的暴露数量和分散程度。此外,MgAl_2O_4与Co_3O_4相互作用提升了Co_3O_4颗粒表面Co~(3+)/Co~(2+)和O_(ads)/O_(latt)的比例,并削弱了Co-O键键能,从而提升了其对丙烷的催化燃烧活性。当Mg负载量为15%(质量分数)时,在Co/MgO(15%)/γ-Al_2O_3-TiO_2催化剂上进行丙烷燃烧,丙烷90%转化率的温度比无Mg掺杂的Co/γ-Al_2O_3-TiO_2催化剂的降低了45℃,并且连续反应40 h其活性保持稳定。 相似文献
15.
Hydrogen and fluorine addition reactions with C 28( Td) have been investigated by the density function theory method at B3LYP/6-31G level. The interaction potential between C 28( Td) and atom X (X=H and F) shows that there are three possible stable isomers of C 28( Td)X (X=H and F) and the average binding energy calculations suggest that C 28( Td)H 4 is the most stable hydrogen adduct among C 28( Td)H n ( n=1–28). Furthermore, by comparisons of the energy between C 28( Td)H and C 28( Cs)H we found that the former are more stable than the later, and the structural and energy analysis further indicate that C 28( Cs)H is only with a small distortion of C 28( Td)H symmetry. In addition, the transition states, as well as reaction pathways of X transfer reactions between different key points on C 28( Td) representative patch are given to explore the possible reaction mechanism. 相似文献
16.
以溶胶凝胶法制备了CuO/CuAl 2O 4、Co 3O 4/CoAl 2O 4以及Mn 2O 3/Al 2O 3氧载体,在流化床反应器中CO 2气氛下研究了不同温度下氧载体释氧特性,并通过分析得到各氧载体的释氧动力学机理函数、活化能及指前因子等重要参数。释氧过程中,氧载体CuO/CuAl 2O 4中CuO、CuAl 2O 4均为活性相,释氧后转化为Cu 2O及CuAlO 2,而Co 3O 4/CoAl 2O 4及Mn 2O 3/Al 2O 3中CoAl 2O 4和Al 2O 3均为惰性相,仅有Co 3O 4和Mn 2O 3参与释氧并分别转化为CoO和Mn 3O 4。三种氧载体的释氧过程均可由成核-核生长机理描述,释氧初期氧载体经化学反应形成新的活性核心,随后活性核心聚集形成还原态的氧载体团簇。各氧载体释氧的机理函数G(x)有不同的表达式,CuO/CuAl 2O 4、Co 3O 4/CoAl 2O 4、Mn 2O 3/Al 2O 3释氧的活化能E分别为226.37、130.06和65.90 kJ/mol,相对应的指前因子A分别为2.99×10 6、4.96×10 3和27.37 s -1。 相似文献
17.
The standard deviation of the Δ Y-values of an analytical line pair is discussed in function of the correlation and orthogonal regression coefficients as well as of the standard deviations of Yx and Yr. It was stated that the orthogonal regression coefficient depends on the ratio sx/sr. A criterium is set up for choosing the right analytical line pair. The optimal field for the values sδy is given in function of the ratio sx/sr as well as of the correlation coefficient. 相似文献
18.
The syntheses of the 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′ 3tach)Cl 2] (M = Ti or Zr (NMR only); R = Bu t or 2,6-C 6H 3Pr i2; R′ = Me or Bu t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu t)(Me 3tach)(CH 2Ph) 2]. The tert-butylimido ligand in [Ti(NBu t)(Me 3tach)Cl 2] undergoes exchange with ArNH 2 (Ar = 4-C 6H 4Me or 2,6-C 6H 4Me or 2,6-C 6H 3Pr i2) to form the corresponding arylimides [Ti(NAr)(Me 3tach)Cl 2]. The Me 3tach ring in [Ti(NR)(Me 3tach)Cl 2] undergoes slow exchange with Bu t3tach or Me 3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu t3tach)Cl 2] and [Ti(NR)(Me 3tacn)Cl 2], respectively. The complexes [Ti(NR)(Me 3tach)X 2] (R = Bu t or 2,6-C 6H 3Pr i2; X = Cl or CH 2Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me 3tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu t3tach)Cl 2] (R = Bu t or 2,6-C 6H 3Pr i2) and [Ti(NBu t)(Me 3tach)(X) 2] [X= Cl or CH 2Ph) are reported. Me 3tach and Bu t3tach = 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane, respectively. 相似文献
19.
Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen ( 1Δ g and 1Σ g+) were calculated for a number of conditions. For the gas phase we estimate K eq( 1Δ g3Σ g-) = 1.67 exp(-94.31 KJ/RT) and K eq( 1Σ g+/ 3Σ g-) = 0.33 exp(-157.0 KJ/RT). The calculated rate constants for the 3Σ g+→ 1Δ g transition of O 2 at 25°C varied from 2.5 × 10 -11 s -1 in water to 4.8 × 10 -16 s -1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro-oxidant effect. 相似文献
20.
The enthalpy change for anabolism is needed to model the growth/respiration relation in plants. If all CO 2 production is assigned to catabolism, the anabolic reaction becomes C substrate→C products+ xO 2 with an enthalpy change, Δ Hb. Four methods are proposed for determining Δ Hb: (a) From the difference in the heats of combustion of substrate and anabolic products (i.e. newly grown tissue). (b) From the composition of newly grown tissue and application of Thornton’s rule. (c) From independently measured values of the specific growth rate, RSG, and of the product ( RSG Δ Hb). The product ( RSG Δ Hb) equals (−Δ HCO2RCO2− Rq) where RCO2 is the specific rate of CO 2 production by respiration, Δ HCO2 is the heat of combustion of respiratory substrate per mole of CO 2 and Rq is the specific metabolic heat rate. Δ Hb is then calculated as the ratio ( RSG Δ Hb)/ RSG. (d) From (Δ Hb=−( Rq/ RCO2+Δ HCO2) [(1−)/] where is the substrate carbon conversion efficiency obtained from a total carbon balance. The first three methods have been tested and compared on oat seedlings and the last on corn seedlings. Δ Hb values from all four methods are in reasonable agreement despite the different assumptions involved. 相似文献
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