Theoretical study of molecular hydrogen clusters

Hydrogen clusters are formed by packing H₂ molecules. A structural characterization of (H₂)_N clusters up to N=35 has been carried out at zero temperature by using density functional theory. The binding between the hydrogen molecules is very weak and the cluster growth reminds that of the inert gas clusters. An icosahedron is obtained for (H₂)₁₃. For clusters larger than (H₂)₁₃ several growth models have been compared. The binding energy indicates specially stable clusters for some particular sizes. The magic numbers can be related to Raman spectroscopy experiments, where the intensity of the Raman signal serves to assign enhanced abundance to clusters with N≈13,32,55, which coincide with some of the most stable clusters obtained in the present study. In addition, comparison of theory and experiment suggests that clusters with N smaller than 27 are liquid. The photoabsorption spectra have been calculated using time-dependent density functional theory. Those spectra can be interpreted as a widening of the absorption peaks of the H₂ molecule due to the various environments experienced by different molecules in the same cluster.     

多条转动拉曼谱线雷达测量对流层大气温度

由于对流层大气中气溶胶的存在,传统的利用大气中瑞利散射和振动拉曼散射测量大气温度的方法具有一定的局限性,然而利用大气N₂和O₂分子的的转动拉曼信号获得大气温度信息的方法不受对流层大气中气溶胶的影响。因此利用N₂和O₂分子纯转动拉曼散射激光雷达开展了测量对流层下部温度分布的实验研究。现有的转动拉曼雷达系统基本上是通过获取单一的转动拉曼谱线来反演大气温度,这就导致了系统的信噪比低,不能很好的反演温度。作者在双光栅单色仪的基础上提出了一种新的雷达信号分光系统。这种新的分光系统的每条通道所获得的信号并不是单独的转动拉曼谱线,而是多条转动拉曼谱线之和,这样就能提高整个系统的信噪比。在较小的激光能量和小口径望远镜的情况下,利用这种方法,雷达系统可以在几公里内获得较好的信噪比。最后实验得到了对流层0.3～5 km高度内的大气温度分布, 它与球载无线电探空仪比较, 二者一致性较好。     

温度扰动下CuCl2/DMF溶液的二维相关拉曼光谱分析

溶液的光谱研究一直受到化学工作者的关注,但大多研究是以一维光谱技术为主,存在分辨率低,误差较大,重叠峰难以分辨等诸多弊端,无法清晰地给出需要的信息。二维光谱通过对外部扰动下的动态光谱进行相关分析计算,从而得到光谱强度的整体变化信息,显著提高一维光谱的分辨率以及重叠峰的分离度。在判断特定外扰下不同官能团的响应次序以及研究分子间、分子内的弱相互作用上具有独特优势。采用二维相关拉曼光谱和理论计算相结合,对溶液内微观团簇及其变化进行了研究。利用显微共焦激光拉曼光谱仪对目标溶液(纯DMF与0.84 mol·L-1的CuCl₂/DMF溶液)进行了升温实验。结果发现在C-N键伸缩振动谱带范围内,由于CuCl₂的加入,特征峰强度整体大幅下降,峰宽变大,在1 115 cm-1有新峰产生,随温度升高,伸缩振动峰强度逐渐下降,峰形变缓。为了获得C-N键振动内各特征峰随温度的变化情况,采用移动窗口二维拉曼(MW2D Raman)光谱技术,对光谱数据进行分析。结果表明溶液内不同类别的微观团簇对温度的敏锐程度不同,随温度升高,它们之间存在相互转化,且变化速度不同。为了获取溶液内各微观团簇运动的实质,以温度为外扰,采用二维拉曼(2D Raman)光谱对目标溶液进行分析,通过对二维光谱中特征峰进行归属和变化次序判断,发现金属Cu2+的加入,使得溶液体系变得更加复杂,除存在原溶剂内所含的团簇构型,还存在与Cu2+发生溶剂化的团簇构型,它们之间存在着一定的相互转化。利用密度泛函理论对溶液中可能存在的团簇构型进行结构优化和热力学计算,结果证实了Cu2+与DMF存在相互作用,且由此产生的团簇构型[Cu(DMF)_n]2+(n=1~6)的稳定性随n的增大逐渐变差,进一步验证了二维相关光谱分析的可行性与正确性。     

Resonance and composition effects on the Raman scattering from silver-gold alloy clusters

Low-frequency Raman scattering experiments have been performed on thin films consisting of pure gold or gold-silver alloy clusters embedded in alumina matrix. It is clearly shown that the quadrupolar vibrational modes are observed by Raman scattering because of the effect of resonance with the excitation of the electronic surface dipolar plasmon. This is due to the strong coupling between the collective electronic dipolar excitation and the quadrupolar vibrational modes. This effect of resonance does not exist with the core electron excitations. The mixing of the conduction electron dipolar excitation (surface plasmon) with the core electrons leads to the quenching of the resonant Raman scattering. Received 16 November 2000     

(MgC)n (n=1~10)团簇结构稳定性及金属性第一性原理研究

采用基于密度泛函理论的第一性原理对同比例二元团簇(MgC)n (n=1~10)的结构稳定性和金属性进行比较系统的研究。结果显示：当原子总数N=2, 4, 6, 8, 12时,二元团簇的结构为平面形状,其余为对称性较低的三维构型,且Mg3C3为幻数结构。另外,在二元团簇的形成过程中,镁、碳原子并不是均匀分布于空间中,而是首先形成各自倾向的构型,再结合成团簇。同时,(MgC)n (n=1~10)二元团簇的基态结构在原子总数N=10时发生突变,由平面形向三维结构转变。此外,最高占据轨道和最低未占据轨道间的能隙值除N=8外呈逐渐降低的趋势,说明在同比例二元团簇随尺寸增加的演化中出现半导体性与金属性间的相互转变行为。     

薄膜沉积过程中TiO_2的金红石相向锐钛矿相转变

用ＲＦ磁控放电方法以纯金属钛做靶材在氩氧混合气体中制备了ＴｉＯ２薄膜,Ｒａｍａｎ光谱测量表明,在２Ｐａ工作气压下制备的ＴｉＯ２薄膜为锐钛矿结构,而在０２Ｐａ工作气压下制备的是金红石结构。工作气压的改变引起了ＴｉＯ２薄膜沉积中的相转变。     

(MgC)n (n=1~10)团簇结构稳定性及金属性第一性原理研究

采用基于密度泛函理论的第一性原理对同比例二元团簇(MgC)n (n=1~10)的结构稳定性和金属性进行比较系统的研究。结果显示：当原子总数N=2, 4, 6, 8, 12时,二元团簇的结构为平面形状,其余为对称性较低的三维构型,且Mg3C3为幻数结构。另外,在二元团簇的形成过程中,镁、碳原子并不是均匀分布于空间中,而是首先形成各自倾向的构型,再结合成团簇。同时,(MgC)n (n=1~10)二元团簇的基态结构在原子总数N=10时发生突变,由平面形向三维结构转变。此外,最高占据轨道和最低未占据轨道间的能隙值除N=8外呈逐渐降低的趋势,说明在同比例二元团簇随尺寸增加的演化中出现半导体性与金属性间的相互转变行为。     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

用激光拉曼光谱研究液态乙醇的水合作用过程

为研究室温下乙醇-水二元混合物内部的分子间缔合情形,测得了不同体积配比溶液的拉曼光谱,发现位于2 800~3 050 cm-1波数区间的C—H伸缩振动频率随乙醇中加入水量的增加整体呈现蓝移趋势,而位于1 048 cm-1附近的CO伸缩振动频率的变化规律却与此相反。分析认为,这种现象主要由溶液内部分子间发生的不同水合作用所致,并据此阐明了液态乙醇的水合作用过程:水分子首先与纯乙醇中的自缔合短链发生氢键缔合作用,形成了含有较多乙醇分子数的乙醇水合团簇,直到溶液中水的体积含量达到50%时,乙醇的水合作用达到暂时饱和;而当水的体积含量继续增加到70%以后,水分子致使原有乙醇水合团簇解离形成较小尺寸的团簇,并与解离点位上的乙醇分子羟基发生进一步水合作用;而后,当水体积含量增至一定程度后,还会导致乙醇分子疏水基CH基团与水分子间形成弱氢键C—H…O。     

(OsnN)0,±(n=1-6)团簇电子结构与光谱性质的理论研究

采用密度泛函理论中的杂化密度泛函B3LYP方法在赝势基组LANL2DZ水平上对Os_nN^0,±(n=1-6)团簇的各种可能构型进行了几何结构优化,得出了它们的基态构型,并对基态结构的磁学性质、自然键轨道(NBO)、光谱和芳香性进行了理论研究. 研究结果表明:OsN^-和Os₅N^-团簇发生了"磁矩猝灭"的现象,在Os₂N和Os₄N< 关键词： nN^0,±(n=1-6)团簇')" href="#">Os_nN^0,±(n=1-6)团簇 电子结构 光谱性质 密度泛函理论     

Bridging the gap between small clusters and nanodroplets: spectroscopic study and computer simulation of carbon dioxide solvated with helium atoms

High resolution infrared spectra of He(N)-CO2 clusters with N up to 17 have been studied in the region of the CO2 nu(3) fundamental band. The B rotational constant initially drops as expected for a normal molecule, reaching a minimum for N=5. Its subsequent rise for N=6 to 11 can be interpreted as the transition from a normal (though floppy) molecule to a quantum solvation regime. For N>13, the B value becomes approximately constant with a value about 17% larger than that measured in much larger helium nanodroplets. Quantum Monte Carlo calculations of pure rotational spectra are in excellent agreement with the measured B in this size range and complement the experimental study with detailed structural information. For a larger cluster size (N=30-50) the simulations show a clear sign of convergence towards the nanodroplet B value.     

(BN)25团簇的结构与性能

采用密度泛函理论的杂化密度泛函（B3LYP）方法,在6-31G （d）基组水平上,对（BN）₂₅团簇进行结构优化和频率计算,得到基态构型,并对其稳定性、自然键轨道（NBO）、振动光谱和NICS进行计算.结果表明：（BN）₂₅团簇的能隙值较高,具有良好的化学稳定性;B原子和N原子的内部及原子之间都会发生s、p轨道杂化,原子之间有少量电荷转移;（BN）₂₅团簇的红外光谱和拉曼光谱都有较多振动峰;（BN）₂₅团簇具有芳香性.     

乙醇溶剂中2-巯基苯并噻唑吸附于铁表面的SERS光谱研究

利用共焦显微拉曼系统研究了乙醇溶剂中2 巯基苯并噻唑(HMBT)在不同pH条件下吸附在ORC法粗糙化处理所得铁表面的SERS光谱。结果表明2 巯基苯并噻唑分子在酸性和中性溶液中通过环外S或环内N原子吸附于铁表面,而在碱性溶液中分子失去氢原子,并通过静电相互作用吸附于铁表面上。     

PdCl_2/SiO_2和Pd-B/SiO_2非晶态合金催化剂的Raman光谱表征

采用共焦显微Ｒａｍａｎ光谱和Ｘ－射线衍射方法表征了负载型ＰｄＣｌ２／ＳｉＯ２和Ｐｄ－Ｂ／ＳｉＯ２非晶态合金催化剂的结构。结果表明ＰｄＣｌ２分散在ＳｉＯ２载体上后,与载体表面的相互作用使其在室温时即发生β→α构型转变。Ｐｄ－Ｂ／ＳｉＯ２非晶态合金的Ｒａｍａｎ光谱在３００－５００ｃｍ－１区域内呈现一大的弥散峰。与无负载Ｐｄ－Ｂ非晶态合金比较初步认定该弥散峰与Ｐｄ－Ｂ键振动有关,温度升高Ｐｄ－Ｂ／ＳｉＯ２催化活性下降,其主要原因为Ｐｄ－Ｂ／ＳｉＯ２非晶态合金在高温下逐渐晶化为Ｐｄ金属所致。ＰｄＣｌ２与ＳｉＯ２载体表面的相互作用使其具有较高的分散性,由此还原制备的Ｐｄ－Ｂ／ＳｉＯ２非晶态合金较之无负载Ｐｄ－Ｂ非晶态合金更加微细化,因而具有更大的活性比表面     

Radiolysis of mixed KI + RbI and KI + CsI powders

Abstract

Pure and mixed powders of KI + RbI and KI + CsI are irradiated by X-rays at room temperature. V-type defects are identified by means of Raman scattering experiments. Raman spectra show that similar defects are obtained in pure powders or crystals. Iodine molecules are stabilized in KI in the form of large clusters (I₂)_n while I³ _- ions are obtained in RbI and CsI.     

Dual-pump dual-broadband coherent anti-Stokes Raman scattering in reacting flows

A dual-pump, dual-broadband coherent anti-Stokes Raman scattering system for simultaneous measurements of temperature and concentrations of N2, O2, and CO2 in reacting flows is demonstrated. In this system pure rotational transitions of N2-O2 and rovibrational transitions of N2-CO2 are probed simultaneously with two narrowband pump beams, a broadband pump beam, and a broadband Stokes beam. The main advantage of this technique is that it permits accurate temperature measurements at both low and high temperatures as well as concentration measurements of three molecules.     

Sin－1N和Sin－2N2（n=3~9）团簇结构与光振动能谱

用密度泛函理论(Density Functional Theory,DFT)的B3LYP/ 6-311G(d)方法,对Sin－1N和Sin－2N2 (n=3~9)团簇的几何构型、总能量、光振动能谱等性质进行了理论研究.通过对基态结构的几何参量分析发现,对Sin－2N2 (n=3~9)团簇,只有在SiN2和Si2N2结构中N-N成键;n＞4团簇结构,N-N不成键.对团簇能量讨论的结果表明;对于Sin－1N (n=3~9)团簇,总原子数是偶数的团簇比奇数的稳定;对于Sin－2N2(n=3~9)团簇,总原子数是奇数的团簇比偶数的稳定.     

Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented.In all crystals, the Raman active T2g vibration mode of CaF2 was observed, whose frequency shift and fullwidth at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice.Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U6+:CaF2crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.     

从头计算对GanNm团簇的结构与稳定性的研究

用B3LYP-DFT方法对GanN2(n=1~7)和GanN(n=2~8)团簇的结构与稳定性进行了研究.在6-31G*水平上进行了结构优化和频率分析,得到了GanN2(n=1~7)和GanN(n=2~8)团簇的基态结构.在GanN(n=2~8)团簇的基态几何结构中,N原子处在分子结构的中心;在GanN2(n=1~3)团簇中,N—N键比Ga—N键强;在GanN2(n=4~7)团簇中存在Ga3N单元和Ga4N单元.在GanN2(n=1~7)和GanN(n=2~8)团簇中,Ga4N2,Ga6P2,Ga3N,Ga5N和Ga7N较其它团簇稳定.     

The influence of divalent metal ions on low pH induced LacDNA structural changes as probed with UV resonance Raman spectroscopy

UV (275 nm) resonance Raman spectra of LacDNA 22‐mer duplex [d(TAATGTGAGTTAGCTCACTCAT) · d(ATGAGTGAGCTAACTCACATTA)], which contain protein binding sites within the E. coli lac promoter, were measured at two pH values (6.4 and 3.45) in the absence and presence of Mn²⁺ and Ca²⁺ metal ions, respectively. Also, the UV (275 nm) resonance Raman markers of the corresponding oligonucleotide d(TAATGTGAGTTAGCTCACTCAT) and of its complementary anti‐sense strand d(ATGAGTGAGCTAACTCACATTA) were established and tentatively assigned. Large changes in the UV (275 nm) resonance Raman spectra of LacDNA duplex were observed at pH 3.45 as compared with the corresponding spectrum at pH 6.4, in the absence of divalent metal ions and at low concentrations of Ca²⁺ ions, respectively. Major changes comprise: adenine protonation, GC base pair protonation, DNA bases unstacking and changes in the hydrogen bonding strength between the strands of different LacDNA complexes, respectively. Divalent metal ions (Mn²⁺ and Ca²⁺) were found to inhibit LacDNA protonation even at low concentrations. Manganese(II) ions are much more effective in this regard, as compared with calcium(II) ions. Binding of Mn²⁺ ions to N7 of guanine and, possibly, in a lesser extent to adenine was observed as judging from the difference Raman bands at 1315, 1354 and 1493 cm⁻¹. Copyright © 2013 John Wiley & Sons, Ltd.