Quantum experimental evidence

Section 4.04.1.2.1). The spectroscopic and the diffraction results refer to molecules in different vibrational quantum states. In neither case are the- distances those of the hypothetical minimum of the potential function (the optimized geometry). Nevertheless, the experimental evidence appears to be strong enough to lead to the conclusion that the electron redistribution, which takes place upon transfer of a molecule from the gas phase to the crystalline phase, results in experimentally observable changes in bond lengths. 

Concept of quantum-mechanical tunnelling in proton-uansfer reactions introduced (without experimental evidence) by several authors. 

There is convincing experimental evidence for the following important statement. To a degree of approximation satisfactory for most analytical work, the mass absorption coefficient of an element is independent of chemical or physical state. This means, for example, that an atom of bromine has the same chance of absorbing an x-ray quantum incident upon it in bromine vapor, completely or partially dissociated in potassium bromide or sodium bromate in liquid or solid bromine. X-ray absorption is predominantly an atomic property. This simplicity is without parallel in absorptiometry. 

These conditions suffice to determine the possible values of m and n3. As was shown by Pauli, they are compatible with the experimental evidence, and explain many previously difficultly explicable facts involving the exclusion of certain quantum states.f... 

In addition to size, an atomic orbital also has a specific shape. The solutions for the Schrodinger equation and experimental evidence show that orbitals have a variety of shapes. A second quantum number indexes the shapes of atomic orbitals. This quantum number is the azimuthal quantum number (1). 

Named for the Austrian physicist Wolfgang Pauli (1900-1958), this principle can be derived from the mathematics of quantum mechanics, but it cannot be rationalized in a simple way. Nevertheless, all experimental evidence upholds the idea. When one electron in an atom has a particular set of quantum numbers, no other electron in the atom is described by that same set. There are no exceptions to the Pauli exclusion principle. 

When quantum calculations, at the ab initio and at the semiempirical level, gained foot in the realm of chemistry, a steadily increasing number of experimentalists began to use quantum calculations as a supplement in the exposition of their findings. In many case this was - and still is - nothing more that an ornament, like decorations on a cake. This use of quantum chemistry has been, in general, harmless, because results in contrast with experimental evidence have been rarely published, and this production may be considered now as a sort of advertising for the new-born computational chemistry. A more serious use of the facilities offered by the computational techniques is done by scientists provided of... 

There is no experimental evidence for 7r-complexation of arenes to gold centers in the condensed phase. Quantum-chemical calculations were carried out on various levels of theory for 1 1 and 2 1 complexes of benzene and substituted benzenes with Au+ in the gas phase. For all model systems investigated, it has been predicted that an -coordination to a single carbon atom is the ground state of the cation (Cy-symmetry for [(C6H6)Au]+ and 6 -symmetry for [(C6H6)2Au] ). Similar results were obtained for hexafluorobenzene, for which a coordina-... 

Unfortunately, determination of rates of photochemical reactions is often very laborious and besides, for many practical purposes, quantum yields are of great interest. The best that can be done at present probably is to be aware of the existence of the various pitfalls, to exclude as many of them as possible on the basis of available experimental evidence, and to try a correlation with quantum yields anyway. 

Another aspect that has been theoretically studied109,124,129 is experimental evidence that Diels-Alder reactions are quite sensitive to solvent effects in aqueous media. Several models have been developed to account for the solvent in quantum chemical calculations. They may be divided into two large classes discrete models, where solvent molecules are explicitly considered and continuum models, where the solvent is represented by its macroscopic magnitudes. Within the first group noteworthy is the Monte Carlo study... 

The intensity of the fluorescence emission detected at the photodetector stage was plotted as a function of temperature over the same range, and this is shown in Figure 11.22. It falls off rapidly with temperature increase over the whole temperature region. This does not contradict the experimental evidence of Burns and Nathan(56) who showed that the fluorescence quantum efficiency of the ruby fluorescence integrated over the entire band from 620 to 770 nm is independent of temperature (to 5%) in the region from-196 to 240°C, for the emission detected here is only the A-line part of the total fluorescence emission. 

As you learned from the previous section, three quantum numbers—n, 1, and mi—describe the energy, size, shape, and spatial orientation of an orbital. A fourth quantum number describes a property of the electron that results from its particle-like nature. Experimental evidence suggests that electrons spin about their axes as they move throughout the volume of their atoms. Like a tiny top, an electron can spin in one of two directions, each direction generating a magnetic field. The spin quantum number (mj specifies the direction in which the electron is spinning. This quantum number has only two possible values or —... 

Nevertheless, there are two highly efficient CL systems which are believed to involve the CIEEL mechanism in the chemiexcitation step, i.e. the peroxyoxalate reaction and the electron transfer initiated decomposition of properly substituted 1,2-dioxetanes (Table 1)17,26 We have recently confirmed the high quantum yields of the peroxyoxalate system and obtained experimental evidence for the validity of the CIEEL hypothesis as the excitation mechanism in this reaction. The catalyzed decomposition of protected phenoxyl-substituted 1,2-dioxetanes is believed to be initiated by an intramolecular electron transfer, analogously to the intermolecular CIEEL mechanism. Therefore, these two highly efficient systems demonstrate the feasibility of efficient excited-state formation by subsequent electron transfer, chemical transformation (cleavage) and back-electron transfer steps, as proposed in the CIEEL hypothesis. 

Absence of quantum interference in liquids experimental evidence... 

The experimental evidence, then, suggests that quantum interference is absent in liquid metals. At first sight this might seem to contradict Ziman s (1961) theory of liquid metals, in which waves scattered by different atoms do interfere this, however, is not so. Following arguments of Baym (1964), Greene and Kohn (1965) and Faber (1972), one should not use in that theory the Fourier transform S(k) of the instantaneous pair-distribution function, but rather... 

T. P. Softley I would like to ask Prof. Jungen if there is any experimental evidence for the need to include singlet-triplet interaction in a quantum defect description of H2 ... 

Cytosine as well as the other heterocyclic nucleic acid bases are quasiaromatic compounds, expected to be planar. The experimental evidence shows that this is not strictly so, but the deviations of the ring atoms of cytosine from planarity are, in general, small, and in most cases within the limits of the experimental accuracy. Oxygen and amino groups, and the atoms of substituents, when present, appear to deviate more from planarity. In all the quantum-mechanical studies the cytosine ring has been assumed to be planar. 

Transient Photoconductivity. A solution of neutral molecules in a polar solvent shows only ohmic conductivity, but if ions are formed by the action of the photolytic flash these charge carriers generate an additional current which is proportional to the ion concentration. The observation of such transient photocurrents is the most direct experimental evidence for the formation of free, solvated ions in electron transfer reactions. The quantum yield of ion formation can be obtained through proper calibration procedures and the kinetics of ion recombination can be determined. Figure 7.37 gives an example of such transient photocurrent rise and decay. 

In the development of the concepts of atomic structure much of the experimental evidence came from optical and x-ray spectroscopy, From this work certain notations have arisen that are now an accepted part of the language. For example, the n = I shell is sometimes known as the K-shell, the n 2 shell as the L-shell. the it = 3 shell as the JM-shell. etc., with consecutively following letters of the alphabet being used to designate those shells with successively higher principal quantum numbers. A Roman numeral subscript further subdivides the shells in accordance with the n, J, and j quantum numbers of the electrons, as shown in Table 4,... 

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