Electronic origin

The productdepends on the properties of the region from which the two electrons originate and is called the... 

Photoelectron peaks are labelled according to the quantum numbers of the level from which the electron originates. An electron coming from an orbital with main quantum number n, orbital momentum / (0, 1, 2, 3,. .. indicated as s, p, d, f,. ..) and spin momentum s (+1/2 or -1/2) is indicated as For every orbital momentum / > 0 there are two values of the total momentum j = l+Ml and j = l-Ml, each state filled with 2j + 1 electrons. Flence, most XPS peaks come in doublets and the intensity ratio of the components is (/ + 1)//. When the doublet splitting is too small to be observed, tire subscript / + s is omitted. 

Figure Cl.5.2. Fluorescence excitation spectra (cps = counts per second) of pentacene in /i-teriDhenyl at 1.5 K. (A) Broad scan of the inhomogeneously broadened electronic origin. The spikes are repeatable features each due to a different single molecule. The laser detuning is relative to the line centre at 592.321 nm. (B) Expansion of a 2 GHz region of this scan showing several single molecules. (C) Low-power scan of a single molecule at 592.407 nm showing the lifetime-limited width of 7.8 MHz and a Lorentzian fit. Reprinted with pennission from Moemer [198]. Copyright 1994 American Association for the Advancement of Science.

The requirement of a very sharjD and strong electronic origin absorjDtion line limits the technique to strongly absorbing and fluorescing, relatively rigid cliromophores and matrices having little Franck-Condon activity in low-frequency... 

If Iq is the flux of electrons originating at depth d, the flux emerging without being scattered, exponentially decreases with depth according to... 

The total energy is lowered by the interaction. The twTo electrons originally in 7tCH3 nowr occupy an orbital in wrhich there is a slight admixture of py character. The stabilization can be thought of as arising from the electronic delocalization. 

Short Term Noise consists of base line perturbations that have a frequency that is significantly higher than the eluted peak. Short term detector noise is not often a serious problem m liquid chromatography as it can be easily removed by an appropriate noise filter without affecting the profiles of the peaks. Its source is usually electronic, originating from either the detector sensor system or the amplifier. 

Fig. 1. Summary of interactions in LCs and their molecular electronic origin...

The maintenance of a connection to experiment is essential in that reliability is only measurable against experimental results. However, in practice, the computational cost of the most reliable conventional quantum chemical methods has tended to preclude their application to the large, low-symmetry molecules which form liquid crystals. There have however, been several recent steps forward in this area and here we will review some of these newest developments in predictive computer simulation of intramolecular properties of liquid crystals. In the next section we begin with a brief overview of important molecular properties which are the focus of much current computational effort and highlight some specific examples of cases where the molecular electronic origin of macroscopic properties is well established. 

It is concluded that the cooperative effect observed is of long-range nature and therefore of elastic rather than of electronic origin. Recently, the additional suggestion has been made [138] that, due to intermolecular interactions in the crystal environment of [Fe(ptz)g](BF4)2, domains of iron(II) complexes interconvert together. The observed kinetics would then correspond to a first- or higher-order phase transition rather than to the kinetics which are characteristic for the conversion of isolated molecules. 

In bonding to the ligand the metal is always shifted away from the boron and interacts most strongly with C-4. This slip distortion is larger than expected considering the difference between the covalent radii of boron and carbon alone (22), and thus must partially be of electronic origin (cf. refs. 36 and 37). 

Ernsting, N.R, Asimov, M., and Shaefer, F.R (1982) The electronic origin of the p-p absorption of amino coumarins studied in a supersonically cooled free jet. Cbem. Pbys. Lett. 91, 231. 

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