Electronics molecular

I have chosen to begin this book on molecular electronics with the business section. If that does not interest you, I understand. Simply skip on to Chapter 2 where a light introductory hors d oeuvre to molecular electronics is served followed by -350 pages of gut-filling scientific beef for the chemist, surface scientist, device physicist, computer scientist and applied mathematician, in that order. 

This chapter is written in somewhat of a personal letter format, from an academic scientist to my academic scientist or engineering colleagues. Beginning with an outline on the commercialization landscape for molecular 

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Much of the previous section dealt with two-level systems. Real molecules, however, are not two-level systems for many purposes there are only two electronic states that participate, but each of these electronic states has many states corresponding to different quantum levels for vibration and rotation. A coherent femtosecond pulse has a bandwidth which may span many vibrational levels when the pulse impinges on the molecule it excites a coherent superposition of all tliese vibrational states—a vibrational wavepacket. In this section we deal with excitation by one or two femtosecond optical pulses, as well as continuous wave excitation in section A 1.6.4 we will use the concepts developed here to understand nonlinear molecular electronic spectroscopy. 

Bardeen C J, Yakovlev V V, Wilson K R, Carpenter S D, Weber P M and Warren W S 1997 Feedback quantum control of molecular electronic population transfer Chem. Phys. Lett. 280 151... 

Optical metiiods, in both bulb and beam expermrents, have been employed to detemiine tlie relative populations of individual internal quantum states of products of chemical reactions. Most connnonly, such methods employ a transition to an excited electronic, rather than vibrational, level of tlie molecule. Molecular electronic transitions occur in the visible and ultraviolet, and detection of emission in these spectral regions can be accomplished much more sensitively than in the infrared, where vibrational transitions occur. In addition to their use in the study of collisional reaction dynamics, laser spectroscopic methods have been widely applied for the measurement of temperature and species concentrations in many different kinds of reaction media, including combustion media [31] and atmospheric chemistry [32]. 

In the ideal case for REMPI, the efficiency of ion production is proportional to the line strength factors for 2-photon excitation [M], since the ionization step can be taken to have a wavelength- and state-mdependent efficiency. In actual practice, fragment ions can be produced upon absorption of a fouitli photon, or the ionization efficiency can be reduced tinough predissociation of the electronically excited state. It is advisable to employ experimentally measured ionization efficiency line strengdi factors to calibrate the detection sensitivity. With sufficient knowledge of the excited molecular electronic states, it is possible to understand the state dependence of these intensity factors [65]. 

Ortiz J V 1997 The electron propagator picture of molecular electronic structure Computational Chemistry Reviews of Current Trends vo 2, ed J Leszczynski (Singapore World Scientific) pp 1-61... 

Ratner M and Jortner J 1997 Molecular Electronics (Maiden, MA Biackweii)... 

Z-matriccs arc commonly used as input to quantum mechanical ab initio and serai-empirical) calculations as they properly describe the spatial arrangement of the atoms of a molecule. Note that there is no explicit information on the connectivity present in the Z-matrix, as there is, c.g., in a connection table, but quantum mechanics derives the bonding and non-bonding intramolecular interactions from the molecular electronic wavefunction, starting from atomic wavefiinctions and a crude 3D structure. In contrast to that, most of the molecular mechanics packages require the initial molecular geometry as 3D Cartesian coordinates plus the connection table, as they have to assign appropriate force constants and potentials to each atom and each bond in order to relax and optimi-/e the molecular structure. Furthermore, Cartesian coordinates are preferable to internal coordinates if the spatial situations of ensembles of different molecules have to be compared. Of course, both representations are interconvertible. 

The molecular electronic polarizability is one of the most important descriptors used in QSPR models. Paradoxically, although it is an electronic property, it is often easier to calculate the polarizability by an additive method (see Section 7.1) than quantum mechanically. Ah-initio and DFT methods need very large basis sets before they give accurate polarizabilities. Accurate molecular polarizabilities are available from semi-empirical MO calculations very easily using a modified version of a simple variational technique proposed by Rivail and co-workers [41]. The molecular electronic polarizability correlates quite strongly with the molecular volume, although there are many cases where both descriptors are useful in QSPR models. 

The trends in chemical and physical properties of the elements described beautifully in the periodic table and the ability of early spectroscopists to fit atomic line spectra by simple mathematical formulas and to interpret atomic electronic states in terms of empirical quantum numbers provide compelling evidence that some relatively simple framework must exist for understanding the electronic structures of all atoms. The great predictive power of the concept of atomic valence further suggests that molecular electronic structure should be understandable in terms of those of the constituent atoms. 

This completes our introduction to the subject of rotational and vibrational motions of molecules (which applies equally well to ions and radicals). The information contained in this Section is used again in Section 5 where photon-induced transitions between pairs of molecular electronic, vibrational, and rotational eigenstates are examined. More advanced treatments of the subject matter of this Section can be found in the text by Wilson, Decius, and Cross, as well as in Zare s text on angular momentum. 

E. Kracka, T. H. Dunning, Jr., Advances in Molecular Electronic Structure Theory Calculation and Characterization of Molecular Potential Energy Surfaces T. H. Dunning, Jr. Ed., 129, JAI, Greenwich (1990). 

W. C. Ennler, H. C. Hsieh, Advances in Molecular Electronic Structure Theory T. H. 

GAMESS stands for general atomic and molecular electronic structure system (we reviewed a version dated Dec. 2, 1998). It is an ah initio and semiempirical program, and has seen the most widespread use for ah initio calculations. The ASCII input hie format is usable but somewhat more lengthy than some other programs. The fact that GAMESS is a free, high-quality software makes it a favorite of many academic researchers. 

Molecular modeling has evolved as a synthesis of techniques from a number of disciplines—organic chemistry, medicinal chemistry, physical chemistry, chemical physics, computer science, mathematics, and statistics. With the development of quantum mechanics (1,2) ia the early 1900s, the laws of physics necessary to relate molecular electronic stmcture to observable properties were defined. In a confluence of related developments, engineering and the national defense both played roles ia the development of computing machinery itself ia the United States (3). This evolution had a direct impact on computing ia chemistry, as the newly developed devices could be appHed to problems ia chemistry, permitting solutions to problems previously considered intractable. 

Traditional appHcations for latices are adhesives, binders for fibers and particulate matter, protective and decorative coatings (qv), dipped goods, foam, paper coatings, backings for carpet and upholstery, modifiers for bitumens and concrete, and thread and textile modifiers. More recent appHcations include biomedical appHcations as protein immobilizers, visual detectors in immunoassays (qv), as release agents, in electronic appHcations as photoresists for circuit boards, in batteries (qv), conductive paint, copy machines, and as key components in molecular electronic devices. 

L. R. Dalton and co-workers. Molecular Electronics andMolecular Electronic Devices, CRC Press, Inc., Boca Raton, Fla., 1993, pp. 125—207. 

J. Janata, Phys.Chem.Chem.Phys., 5 (2003) 5155-5158 Organic Semiconductors in Molecular Electronics ... 

Electronics Production of circuit boards (producing contacts in boreholes), modified electrolytic condensers, modified field effect transistors, molecular electronics (unidirectional conductors), photostructural lacquers based on ICPs (electron beam lithography), novel photoluminescent diodes (LED), data storage (e.g. spatially resolved eleclrochromics)... 

A review of what has come to be called molecular electronics (Mirkin and Ratner 1992) includes many striking discoveries, such as a device based on azoben .ene (Liu et al. 1990) that undergoes a stereochemical transition, trans-to-cis, when irradiated with ultraviolet light, but reverts to trans when irradiated with visible light. The investigators in Japan found that L-B films of their molecules can be used for a... 

I ain going to leave you to prove for yourself that the wavefunction corresponding to this infinite-distance H2 problem is a product of two hydrogen atom wavefunc-tions. Physically, you might have expected this the two atoms are independent so the electronic wavefunctions multiply to give the molecular electronic... 

If I write possible atomic orbitals for hydrogen atom A as Xa possible atomic orbitals for hydrogen atom B as the molecular electronic wavefunction will be... 

For the purposes of a purely theoretical analysis of molecular electronic structure, we need more detailed information. The term population analysis was introduced in a series of papers by Mulliken in 1955, but the basic ideas had already been anticipated by Mulliken himself, and by other authors. The technique has been widely applied since Mulliken s 1955 papers, because it is very simple and has the apparent virtue of being quantitative . The word quantitative seems to mean two different things to different authors ... 

Hiickel models of molecular electronic structure enjoyed many years of popularity, particularly the r-electron variants. Authors sought to extract the last possible amount of information from these models, perhaps because nothing more refined was technically feasible at the time. Thus, for example, the inductive effect was studied. The inductive effect is a key concept in organic chemistry a group R should show a - -1 or a —I effect (according to the nature of the group R) when it is substituted into a benzene ring. 

Over the last thirty years, international collaboration and cooperation on a scale rarely witnessed in science has led to the development of several very sophisticated software packages for ab initio molecular electronic structure calculations. In the early days, such packages were freely distributed amongst workers in the field. Today, you buy executable code, a licence and professional documentation just as with any software package. 

Finally, many of the common molecular electronic properties depend only on the chance of finding any electron in dx and this is obviously m times the above quantities. We focus attention on points in space (written r) and interest ourselves in the electron probability density... 

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