Molecular Transitions

Halgren T A and Lipscomb W N 1977 The synchronous transit method for determining reaction pathways and locating molecular transition states Chem. Phys. Lett. 49 225... 

The polarization properties of single-molecule fluorescence excitation spectra have been explored and utilized to detennine botli tlie molecular transition dipole moment orientation and tlie deptli of single pentacene molecules in a /7-teriDhenyl crystal, taking into account tlie rotation of tlie polarization of tlie excitation light by tlie birefringent... 

For condensed species, additional broadening mechanisms from local field inhomogeneities come into play. Short-range intermolecular interactions, including solute-solvent effects in solutions, and matrix, lattice, and phonon effects in soHds, can broaden molecular transitions significantly. 

The Synchronous-Transit Method for determining Reaction Pathways and Locating Molecular Transition States Thomas A. Halgren and William N. Lipscomb Chemical Physics Letters 49 (1977) 225-232... 

Tabic 6-2. Correlation diagram of the C2/, point group of the isolated T6 molecule (left column) with the C2i, factor group for solid T(, (right column) via the site symmetry C group (center). L, M, and N indicate the principal molecular transition dipole moments, while a, b, and c arc the crystalline axes. 

Inclusion complexes of molecular transition metal hosts. T. J. Meade and D. H. Busch, Prog. Inorg. Chem., 1985,33, 59(331). 

All mechanisms proposed in Scheme 7 start from the common hypotheses that the coordinatively unsaturated Cr(II) site initially adsorbs one, two, or three ethylene molecules via a coordinative d-7r bond (left column in Scheme 7). Supporting considerations about the possibility of coordinating up to three ethylene molecules come from Zecchina et al. [118], who recently showed that Cr(II) is able to adsorb and trimerize acetylene, giving benzene. Concerning the oxidation state of the active chromium sites, it is important to notice that, although the Cr(II) form of the catalyst can be considered as active , in all the proposed reactions the metal formally becomes Cr(IV) as it is converted into the active site. These hypotheses are supported by studies of the interaction of molecular transition metal complexes with ethylene [119,120]. Groppo et al. [66] have recently reported that the XANES feature at 5996 eV typical of Cr(II) species is progressively eroded upon in situ ethylene polymerization. 

Application of small metal particles has attracted the attention of the scientists for a long time. As early as in the seventies Turkevich already prepared mono-dispersed gold particles [19], and later, using molecular transition metal carbonyl clusters [20], the importance of small nanoparticles increased considerably. One of the crucial points is whether turnover frequency measured for a given catalytic reaction increases or decreases as the particle size is diminished. 

For adsorbates on a metal surface, an SFG spectmm is a combination of resonant molecular transitions plus a nonresonant background from the metal. (There may also be a contribution from the water-CaF2 interface that can be factored out by following electrode potential effects see below.) The SFG signal intensities are proportional to the square of the second-order nonlinear susceptibility [Shen, 1984] ... 

Wang, S.-Q. Molecular Transitions and Dynamics at Polymer/Wall Interfaces Origins of Flow Instabilities and Wall Slip. VoL 138, pp. 227-276. 

The RTD quantifies the number of fluid particles which spend different durations in a reactor and is dependent upon the distribution of axial velocities and the reactor length [3]. The impact of advection field structures such as vortices on the molecular transit time in a reactor are manifest in the RTD [6, 33], MRM measurement of the propagator of the motion provides the velocity probability distribution over the experimental observation time A. The residence time is a primary means of characterizing the mixing in reactor flow systems and is provided directly by the propagator if the velocity distribution is invariant with respect to the observation time. In this case an exact relationship between the propagator and the RTD, N(t), exists... 

Isotopic shifts for molecular transitions are of order of 1% and thus easy to observe. Suitable molecules with transitions accessible to CRIRES are CO, CN and SiO. The Si isotopes appear particularly interesting as they can provide for a neutron dosimeter during the AGB-phase. Models for the thermonuclear... 

The broadband analysis was confirmed by the experimental results mentioned in Sect. 5.4.1. This method can also be further enhanced by some of the techniques described in Sects. 5.4.2 and 5.4.3. The conclusion is that these methods of microcavity-enhanced optical absorption sensing provide compact, inexpensive, and sensitive detectors for molecular species in the ambient gas or liquid, and that further increases in sensitivity can be implemented to make them even more competitive. The molecular-transition specificity that is implicit in absorption spectroscopy is a limiting restriction, but the surface-enhanced Raman sensing that is enabled by metallic nanoparticles on the microresonator surface can significantly increase the number of molecular species that could be detected. 

A summary of our results on the phase diagram of water is shown in Figure 8. We find that the molecular to non-molecular transition in water occurs in the neighborhood of the estimated ZND state of HMX. This transition shows that the detonation of typical energetic materials occurs in the neighborhood of the molecular to non-molecular transition. 

Catalysts other than homogeneous (molecular) compounds such as nanoparticles have been used in ionic liquids. For example, iridium nanoparticles prepared from the reduction of [IrCl(cod)2] (cod = cyclooctadiene) with H2 in [bmim][PF6] catalyses the hydrogenation of a number of alkenes under bipha-sic conditions [27], The catalytic activity of these nanoparticles is significantly more effective than many molecular transition metal catalysts operating under similar conditions. 

Figure 2.3 Range of electromagnetic radiation. All electromagnetic radiation travels at a constant speed of 3 X 108 ms-1 but the energy associated with each waveform is inversely proportional to the wavelength. The energy required for different atomic and molecular transitions is provided by radiation of different wavelengths.

Ultraviolet radiation will frequently induce which of the following molecular transitions ... 

A comprehensive book on chemistry, structure and bonding of Zintl compounds has been edited by Kauzlarich (1996) in this book several aspects of Zintl phases such as structural patterns, molecular transition complexes of Zintl ions, transition metal Zintl compounds are deeply discussed. 

The high laser intensity enables molecular transitions to be measured even when their Franck-Condon factors are small, so that the fluorescence progression can be followed up to high vibrational levels, thus considerably increasing the accuracy of the molecular constant determination. It furthermore permits fluorescence measurements at low pressures. 

The obtainable small laser linewidth with tunable wavelength (Section II) improves selection of different molecular transitions and in many cases the selective population of a single excited rotational level can be achieved. 

Using this optical Keir cell the authors developed a technique to measure the lifetimes of atomic and molecular transitions on a picosecond time scale 138a), See also the reviews by Rentzepis 138b) about ultrafast processes and Merkelo 138c),... 

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