Molecule Matters van der Waals Molecules

In Part 2 of this series, we discuss homo- and hetero-nuclear noble gas dimers. Experimental and theoretical results for dimers containing He, Ne, Ar, Kr and Xe are reviewed. These dimers are bound by London dispersive forces, which is one component of the van der Waals or intermolecular forces. Though these are usually called van der Waals complexes or van der Waals molecules, these dimers may be more appropriately called London molecules. Heliumdimer is a particularly interesting case with the equilibrium internuclear distance estimated to be about 50 Angstrom.     

van der Waals

In this article, Debye’s contributions to understanding van der Waals attractive forces, specifically, dipole-induced dipole interaction, is discussed. The Rg...HF complex structure is influenced by this interaction. Hence, these types of van der Waals molecules can be more specifically called Debye molecules.     

Molecule matters

Carbon dioxide is a fascinating molecule; its gaseous, liquid, solid and even supercritical fluid states have unique properties and applications. The linear triatomic structure of carbon dioxide molecule with two carbon-oxygen double bonds is all too familiar. However a whole new world has been opened up by high pressure-high temperature experiments that effected the polymerization of this small molecule into a covalent network structure with carbon-oxygen single bonds. The crystalline and amorphous forms of carbonia are built up of linked tetrahedral CO₄ units.     

Molecule matters

4-(N,N-dimethylamino)benzonitrile, popularly known as DMABN, has received tremendous attention for nearly five decades. In this article, we outline some of the features of the molecule that have made it such an interesting system to study, such as fluorescence emission in two wavelengths. The article also highlights how limited our understanding of the excited state structure of a small molecule like DMABN is, despite the availability of various resources to investigate it. Anunay Samanta is a professor of chemistry at the University of Hyderabad. Mainly he is interested in photophysics and time-resolved spectroscopy. Design of fluorosensors and study of photophysical response of molecular systems in ionic liquids are two of his current research topics of interest.     

Molecule matters

The first stable compound with a ‘quintuple bond’ reported recently is an exciting development that raises fundamental questions in theoretical and experimental chemistry.     

Molecule matters

The synthesis of a Fe^VI complex in an octahedral coordination geometry has been achieved recently by Wieghardt and coworkers. This is only the second hexavalent iron complex known after the tetrahedral ferrate ion, [FeO₄]^2?. The synthesis of the new Fe^VI complex involves a low temperature photolysis of an Fe^IV(N₃) precursor which leads to the formation of the Fe^VI complex containing a Fe≡N triple bond. The structural characterization of the Fe^VI complex has been achieved by a variety of spectroscopic techniques including Mössbauer spectroscopy and X-ray absorption spectroscopy. Experimentally it is found that the Fe^VI complex is diamagnetic. Theoretical calculations reveal that the Fe^VI complex has an electronic configuration 3d² (S = 0); the d electrons are paired in a d_xy orbital.     

Molecule matters

Ever since its isolation in 1820, Quinine has played a crucial role in the development of organic chemistry, chemical industry and modern medicine. The total synthesis of quinine, widely regarded as an event of epochal importance was claimed by Woodward and Doering in 1945. This work, however, heavily relied on unsubstantiated literature reports and it appears that Woodward’s work fell short of a total synthesis of quinine. The first stereoselective total synthesis of quinine was accomplished only in 2001, by Stork, who incidentally is the originator of the concept of stereoselectivity in total synthesis. Naturally, this work has been attested as a landmark in organic synthesis by leaders in the field.     

Molecule matters

Divalent carbon compounds which were once considered as highly reactive organic intermediates have been tamed by the modern day synthetic chemist in the form of N-heterocyclic carbenes. The land marks in the history of development of these compounds and their applications as ligands in the Nobel Prize winning work on olefin metathesis catalysts are described. Anil J Elias is a professor at the Department of Chemistry, Indian Institute of Technology, Delhi.     

范德瓦尔斯气体多方过程的研究

推导了范德瓦尔斯气体多方过程的P-V方程,然后推导用温度和熵表示的范德瓦尔斯气体多方过程的过程方程,由此得到范德瓦尔斯气体几种特殊的等值过程的过程方程.     

“发现式”过程教学探讨

通过对“发现式”过程教学的探讨 ,引导学生学习、理解牛顿———莱布尼兹公式 ,开发学生的智力 ,培养学生的能力。     

浅析范德瓦尔斯气体的各种过程

分析了范德瓦尔斯气体的各种过程,推导出了范德瓦尔斯气体的多方过程,并讨论了其它过程方程及相应的多方指数.     

范德瓦耳斯方程的一种推导方法

对吸引刚球模型近似描述的实际气体的正则配分函数作平均场近似处理,在不引入悔逸函数的情况下等效地推导出了范德瓦耳斯状态方程。     

范德瓦耳斯方程与气体分子运动论

介绍了范德瓦耳斯方程的提出背景及其内涵     

圆周上的范德瓦尔登数

The big upper bound of typical van der Waerden number was investigated through calculating the van der Waerden number on a circle. And the van der Waerden number Wh (3,3) = 9, Wh (3,3,3)≥25 on a circle was calculated by computer.     

简谐振子的范德瓦尔斯相互作用研究

本文从谐振子出发,考虑电偶极子-电偶极子的相互作用,采用正则变换,消除交叉项,使之成为两个独立的谐振子,进一步算出两个新谐振子的角频率,还能算出体系的基态能量,并解释范德瓦尔斯相互作用的分离相关性.再用概率论的知识探讨了波函数,解释了存在范德瓦尔斯相互作用而导致能量下降的原因,并计算了两个谐振子的条件概率.     

范德瓦尔登数方程组

SetWh(n,n)=p 1.ItisobviousthatthereexistvanderWaerdennum bersoncirclefromtheexistenceanduniquenessofthe vanderWaerdennumbers,andthefollowingresult holds.Theorem1ForthevanderWaerdennumberson circle,thereholds Wh(n,n)≤W(n,n).TheleftsideoftheinequalityinTheorem1isrigor ouslylessthantherightsideifW(n,n)satisfysome conditions.Theorem2IfthevanderWaerdennumbersW(n,n)=(n-1)a bfor2≤b≤n-2,andn>3,thenWh(n,n)相似文献   

范德瓦耳斯体积改正数的另一种计算方法

范德瓦耳斯体积改正数b不应当是分子体积总和b0的四倍。分子的自由活动空间不仅与分子体积总和及分子处于最紧密状态时的间隙有关，还与分子本身的运动用关。笔得出的结论是b＝6√2／πb0。     

固体中的范德瓦耳斯相互作用研究与应用

介绍固体物理课程的分子晶体中范德瓦尔斯相互作用.概述有关范氏相互作用的研究动态,范氏力的产生根源,推导范氏相互作用势,例举范氏相互作用的具体应用.旨在强调这一领域研究的重要性,精心组织教学内容,激发学生的兴趣.     

范德瓦尔斯频移及线型畸变现象

从理论上研究了囚禁于两电介质间薄原子蒸汽的频率调制吸收光谱中范德瓦尔斯频移及线型畸变现象,发现在频率调制情形下频移很明显,线型则由对称类色散型转为非对称类吸收型。采用频率调制的方法解决了在很多情形下采用直接法或吸收法不易实现对vdW作用势进行精确测量的难题。     

Comments on van der Linden's Critique and Proposal for Equating

While agreeing with van der Linden (this issue) that test equating needs better theoretical underpinnings, my comments criticize several aspects of his article. His examples are, for the most part, worthless; he does not use well‐established terminology correctly; his view of 100 years of attempts to give a theoretical basis for equating is unreasonably dismissive; he exhibits no understanding of the role of the synthetic population for anchor test equating for the nonequivalent groups with anchor test design; he is obtuse regarding the condition of symmetry, requiring it of the estimand but not of the estimator; and his proposal for a foundational basis for all test equating, the “true equating transformation,” allows a different equating function for every examinee, which is way past what equating actually does or hopes to achieve. Most importantly, he appears to think that criticism of others is more important than improved insight that moves a field forward based on the work of many other theorists whose contributions have improved the practice of equating.