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1.
激发态分子内质子转移因其独特的光学性质而受到研究人员的青睐. 然而,关于改变原子电负性对激发态分子内质子转移过程和光物理性质影响的系统研究相对较少. 本文通过理论方法选择了一系列苯并噁唑异硫氰酸酯荧光染料(2-HOB、2-HSB 和2-HSeB),并通过改变氧族原子的电负性,系统地研究了激发态分子内质子转移过程和光物理性质. 计算的键角、键长、能隙和红外光谱分析表明,3个分子的分子内氢键强度依次为2-HOB<2-HSB<2-HSeB. 相应地,势能曲线的能垒大小为2-HOB>2-HSB>2-HSeB. 此外,计算的电子光谱表明,随着原子电负性的降低,发射光谱发生红移. 本工作将为基于激发态分子内质子转移性质的新型染料的合成和应用提供一定的理论指导.  相似文献   

2.
用原子电负性、极化度并结合表征原子空间连接方式的立体效应参数对醚分子中不同环境碳原子的化学位移进行关联,将23个脂肪醚中153个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:δC=121.1348+94.3651Qi-2.0823QiΣαx-7.6347SH-47.6149SO(R=0.9990R2=0.9980S=0.85F=18478.97n=153)上式中Qi表示观测原子的部分净电荷,Σαx表示近邻原子极化度,SH,SO为立体效应参数.方程中各参数计算简单,物理意义比较明确,通过用"留一法"(LOO)检验(Rcv=0.9980,R2cv=0.9977,Scv=0.89)及对模型外4个化合物43个碳原子化学位移的预测值和实验值比较,结果表明模型具有较好的稳定性和预测精度.  相似文献   

3.
通过对二硼化镁及掺杂二硼化镁超导体硬度和电负性进行研究,发现其具有较好的规律性.因此,本文提出用硬度均衡值ηcq和电负性的平均效应值χcq作为掺杂二硼化镁超导电性的一个判断标准,对今后实验工作者掺杂元素和掺杂比例的选取有很好的指导意义.  相似文献   

4.
研究了目前已掺杂的铁基砷化物超导体的硬度和电负性与超导电性的关系,发现其有很好的规律性。因此,提出用硬度均衡值和电负性的平均效应值作为掺杂铁基砷化物超导体超导电性的一个判断标准。  相似文献   

5.
在B3LYP/6-31+G*水平上研究BF4-与甘氨酸间氢键作用特征,并在B3LYP/6-311++G**水平上计算单点能. 对二聚物几何结构、能量、氢键成键特征进行分析. 分子中的原子拓扑分析表明氢键成键原子间存在(3,-1)关键点,电子密度和Laplacian量落在氢键范围内. 进一步对氢键形成导致H原子净电荷、偶极矩、能量及体积的改变进行系统分析.  相似文献   

6.
平衡电负性与烷烃核磁共振碳谱位移   总被引:6,自引:6,他引:0  
定义了烷烃分子中碳原子的平衡电负性(AEE),用平衡电负性和NiH(em=0, α, β, γ)和NjC(j=α, β, γ)结构信息参数研究了烷烃的13C NMR化学位移模型.结果表明,烷烃13C NMR化学位移(CS)可用下式来定量描述:
CS=-1736.776+755.118AEE+5.2539N0H+1.8837NβH-0.2066NγH
用上式估算了99个碳原子的化学位移,标准差为0.9861ppm,平均绝对误差0.78ppm,预测值与实验值十分吻合.  相似文献   

7.
激光溅射锌和镉原子与SO2分子反应的低温基质隔离红外光谱实验表明,在氩和氖的惰性基质中,形成了环式M(SO2)分子及其阴离子M(SO2)- (M=Zn, Cd).相关同位素(34SO2和S18O2)替代实验及密度泛函理论计算均证实了这一结果.此外,自然电荷布居分析表明电子从金属锌和镉的s轨道转移到了SO2配体上形成了M+(SO2)-“离子对”复合物,且该分子中的Zn-O键以及Cd-O键均表现出强的极化共价性.而Hg原子在与SO2反应中所表现出来的惰性可由其较强的相对论效应所致的6s价电子层收缩与高电离电位得以解  相似文献   

8.
使用DFT的B3LYP方法对几种咪唑二氧杂环化合物的分子结构、红外光谱、生成焓、爆轰性能和化学/热稳定性进行了研究.四种不同含能基团-NO2,-NH2,-N3和-ONO2对该化合物各项性能的影响进行了比较.结果表明-NO2和-ONO2基团有效地增加了化合物的密度,而-N3基团极大地增加了化合物的生成焓.其中-NO2取代物爆轰性能接近1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane,-ONO2取代物的爆轰性能低于hexahydro-1,3,5-trinitro-1,3,5-triazine.自然键轨道分析表明,这些化合物中相对较弱的键为取代基和咪唑环之间的键,以及二氧杂环中的C-O键.吸电子基团(-NO2, -N3和-ONO2)在分子中产生了明显的诱导效应,减弱了基团与咪唑环之间的链接,降低了对应键的键裂解能.研究表明基团的电负性与化合物的稳定性有关.考虑到化合物的爆轰性能和热稳定性,DNTNDI化合物满足高能量密度材料的要求.  相似文献   

9.
薛晨  徐衡 《波谱学杂志》2014,31(3):397-406
用一种计算直接键连原子核自旋耦合常数的半经验公式,结合量子化学计算得到的32种有机分子稳定几何构型的7种不同算法下的原子电荷,探究原子电荷算法的不同对1JCH理论计算的影响,拟合出基于7种原子电荷的耦合常数计算公式,并利用拟合公式对5种分子进行了检验.计算结果表明拟合的32种分子及检验的5种分子的耦合常数的计算值均与实验值较好的符合,拟合得到的基于7种原子电荷的计算公式均可以对其他分子体系的耦合常数进行预测.另外,计算结果同样显示原子电荷算法的不同对1JCH理论计算值有一定的影响却不显著,其中基于电荷均衡方法电荷(QEq)得出的耦合常数计算值与实验值的偏差较其它6种原子电荷的小,结果更可靠.  相似文献   

10.
用同一动能(150keV)而不同电荷态的40Arq+(8≤q≤16)离子入射金属Al表面,靶原子受激辐射产生特征光谱线. 实验结果表明:高电荷态离子与金属表面相互作用过程中,经过与靶原子碰撞(Penning碰撞)交换动能和共振电子俘获(resonant capture)释放库仑势能,将携带的能量沉积于靶表面,使靶原子激发. 这种激发不同于光激发,它不仅激发了原子复杂电子组态之间的跃迁,而且跃迁辐射的特征谱线强度增强的趋势与入射粒子的库  相似文献   

11.
Correlations are given between ESCA chemical shifts and partial atomic changes calculated by the modified Sanderson method. Elements included are boron, carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, oxygen, sulfur, selenium, fluorine, chlorine and bromine. Successful correlations were obtained for most elements; the best success was for situations involving a constant number of σ bonds. The method was least successful for nitrogen, oxygen, chlorine and bromine. The modified Sanderson method performed comparably to CNDO and Jolly electronegativity calculations in most cases. Correction for molecular potential is automatically achieved using the modified Sanderson method.When the data for all elements are considered the MS model seems to work reasonably well. Correlations for B, C, Ge, F, N, As and Se seem to be as good as most methods applied to these elements. The MS method works particularly well for Si, Sn, P and S. It is inapplicable to O, Cl and Br.For compounds of elements which exist in more than one formal oxidation state, it is necessary to obtain a separate plot of EB, versus qi for each oxidation state. Once this is done, the calculated and experimental binding energies show good correlation. The slopes and intercepts given in Table 3 may be used for this purpose.The reason for separate correlation lines in the case of multiple oxidation states may be understood when one considers the method by which Sanderson originally calculated his atomic E values. Sanderson's original E values were calculated as the ratio of the electron density of an element stripped of all its valence electrons to the electron density of the corresponding inert gas. By considering only the inert shell configuration, Sanderson's E values are valid for filled electron shell oxidation states. However, no allowance for lone electron pairs is made. Thus, charges calculated by Sanderson's method for elements bound in less than their maximum oxidation state may not be correct relative to other oxidation states of the same element. Attempts to correct for this neglect of lone pairs were made during the course of this work by assigning E values for an electron pair or by calculating E values for non-inert shell valence configurations met with failure.The low slopes of the binding energy-charge correlations for oxygen and the halogens may also be explained by the method Sanderson used to calculate his atomic E values. Sanderson assumed that all elements shared all valence electrons in bonding. This is not the case for the halogens or oxygen which retain essentially inert lone electron pairs. Since the effect of these lone pairs is not specifically dealt with, the charges calculated by Sanderson's method and the MS method are larger than they should be in the case of elements which retain nonbonded lone pairs.Throughout these studies, it has been noted that the MS method needs no correction for molecular potential. This may be explained by the manner in which group E values are calculated. Since the electronegativities of the atoms comprising a group are “sequentially” equalized from the terminal atom of a group inward to the site of the central atom, through bond inductive effects are accounted for. This procedure reduces a multiatom group to a form in which it may be treated as a single atom attached to the atom of interest. In this form, a molecule is reduced to Pauling's “nearest neighbor” picture. Thomas19 has found that Pauling's “nearest neighbor” approximation works well for correlating ESCA data of small (e.g. methane-line) molecules without additional correction for molecular potential. Thus, the MS method has reduced a molecule to a form where the “nearest neighbor” approximation is applicable.The MS method works well for covalent molecules. As was pointed out earlier, the method fails for ionic solids primarily because of anomalies introduced by the Madelung potential. It is speculated that the MS method will work well for isolated ionic molecules in the gas-phase.  相似文献   

12.
The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχve + bPEIfi + c was developed, in which χve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χve and PEIfi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
刘隆鉴  章壮健 《中国物理》2001,10(9):847-852
By studying the average effect of the electronegativity of alloy and compound superconductors, some empirical laws are found. The average value of the electronegativity of alloy superconductors \overlineχ is from 1.3 to 1.9, most of which is concentrated in the region 1.5<\overlineχ<1.8. The \overlineχ of many higher Tc superconductors is nearly 1.60. All these characteristics are similar to element superconductors. The average value of the electronegativity \overlineη of positive valence elements in oxide superconductors is from 1.3 to 1.6, and the average effect of an electronegativity of zero on every element \overlineζ is from 1.75 to 2.00. The mean of \overlineη and \overlineζ is from 1.5 to 1.8. When both \overlineη and \overlineζ are near the limit value (1.3 or 1.6 and 1.75 or 2.00), the material has a very low Tc, even is non-superconductive. The \overlineζ of other compound superconductors is either too high or too low, and the \overlineζ is too low so that the Tc of these superconductors is quite low. Studying the average effect of the electronegativity of non-superconducting compounds further confirms the laws.  相似文献   

14.
Molecular-orbital calculations are performed to elucidate electronic structures and optical properties of lithium clusters in which several K-shell electrons are simultaneously excited to the valence levels. It is shown that relaxation of valence electrons around localized core holes influences the photoabsorption near-edge spectra significantly. The spectra in the excited state are modified from those in the ground state due to the presence of initial core holes. Potential energy surfaces are calculated for core-ionized Li9 z+ clusters, which exhibit bound states for z≤3. The present cluster calculations would serve as prototypical models of laser-excited hollow atom solids with applications to X-ray optics.  相似文献   

15.
Based on the relationship between the heat of formation and the change of valence electronic energy in the formation of a compound from its component atoms, and combined with the relationship between the first ionization potential and the average valence electronic energy, the direct link of ionization potential, Ip, with the heat of formation, ΔH0f, was deduced for organic homologous compounds, that is, where Nve,m is the number of valence electrons in molecule, SVEEx is the sum of valence electronic energy of isolated atoms forming the molecule, the term expresses the initial‐state effect of the molecule, and the symbol Rm represents its final‐state effect (polarizability effect). The above equation was confirmed by the correlations between the ionization potentials and the heat of formation of alkanes, alkenes, monosubstituted alkanes RY (Y = OH, NH2, SH, Cl, Br, and I), in which all the expressions have good correlations with correlation coefficients more than 0.9990. With the obtained correlation equations, the ionization potentials of some monosubstituted alkanes were predicted from their experimental heats of formation. The result provides a new insight into the intercorrelation between the ionization potential and the heat of formation for organic homologous compounds. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
锌-牛血清白蛋白的电荷转移谱带研究   总被引:5,自引:0,他引:5  
研究了1:1锌-牛血清白蛋白体系的差示吸收光谱,使用文献数据计算了组氨酸咪唑基的三个π轨道的光学电负性,利用这些数据归属了Zn^2 离子与牛血清白蛋白所形成的配合物的两条电荷转移谱带,推测它们分别为白蛋白组氨酸咪唑基的π2,π3,轨道向Zn(Ⅱ)离子的LMCT跃迁。  相似文献   

17.
M C R Shastry  K J Rao 《Pramana》1989,32(6):811-820
Silver iodide-based fast ion conducting glasses containing silver phosphate and silver borate have been studied. An attempt is made to identify the interaction between anions by studying the chemical shifts of31P and11B atoms in high resolution (HR) magic angle spinning (MAS) NMR spectra. Variation in the chemical shifts of31P or11B has been observed which is attributed to the change in the partial charge on the31P or11B. This is indicative of the change in the electronegativity of the anion matrix as a whole. This in turn is interpreted as due to significant interaction among anions. The significance of such interaction to the concept of structural unpinning of silver ions in fast ion conducting glasses is discussed. Communication number 593 from Solid State and Structural Chemistry Unit  相似文献   

18.
The electronegativity was defined by Pauling1 as a measure of the power of an atom in the molecule to attract electrons to itself. This concept of electronegativity has undergone radical changes. Recent calculations of electronegativity show2,3 that it is a complex quantity including an important atomic term depending on the charge and hybridization of the atom, and a molecular term depending on the length and the nature of the bonds in the molecule. In a molecular group of the type A-B, B is a halogen atom, say chlorine and A stands for different atoms of a subgroup of the periodic table. Since the nature of the bonds in the molecule AB and the electronegativity of halogen atom, B, is constant for a molecular group, the electronegativity, X, of atom A may be related to the dissociation energy and bond length which in its turn is related to the vibrational constant,ωe, and the reduced mass, μ, of the molecule AB.  相似文献   

19.
杨郁  唐成双  赵一帆  虞一青  辛煜 《物理学报》2017,66(18):185202-185202
利用探针辅助的脉冲激光诱导负离子剥离诊断技术对掺入5%O_2的容性耦合Ar等离子体电负特性进行了诊断研究.首先详细解析了脉冲激光剥离后探针的电信号,分析了探针偏压在低于或高于空间电位下的探针收集信号特征;根据探针偏压与探针收集信号之间的依赖关系,用来描述Ar+O_2等离子体电负特性的等离子体电负度被定义为脉冲激光剥离出的电子电流与偏压高于空间电位的探针收集到的背景电子电流的饱和比值,并对等离子体电负度随放电气压、射频功率以及轴向位置的变化进行了诊断测量.实验结果表明等离子体的电负度随着射频功率的增加而减小、随着放电气压的上升而变大;由于非对称电极的分布特性,在轴向方向上靠近功率电极时等离子体电负度有升高的趋势,这种趋势可能与鞘层边界附近二次电子的动力学行为以及负离子的产生与消失过程有关.  相似文献   

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