Molecule molecular ensemble

AFM has also been used to measure the mechanical properties of single molecules, molecular ensembles (membranes, cells), and surface structures. It has also enabled measurement of adhesion on the nanoscale that may exist between a chemically modified... 

Let us now consider the case where tliere is more tlian one exciton in tlie given molecular ensemble. The presence of two or more excess excitons not only creates two or more holes in tlie ground state (see case (a) above) but it also opens up tlie possibility of two excitons being found on neighbouring molecules. Then tlie following two-stage process can take place [26] ... 

The growing computahonal power available to researchers proves an invaluable tool to investigate the dynamic profile of molecules. Molecular dynamics (MD) and Monte Carlo (MC) simulahons have thus become pivotal techniques to explore the dynamic dimension of physicochemical properhes [1]. Furthermore, the powerful computational methods based in parhcular on MIFs [7-10] allow some physicochemical properhes to be computed for each conformer (e.g. virtual log P), suggesting that to the conformahonal space there must correspond a property space covering the ensemble of all possible conformer-dependent property values. 

For polyatomic molecules the situation is somewhat more complex but essentially the same. The effect of intramolecular motion upon the scattering of fast electrons by molecular gases was first described by Debye3 for the particular case of a molecular ensemble at thermal equilibrium. The corresponding average molecular intensity function can be expressed in the following way ... 

From the point of view of the study of dynamics, the laser has three enormously important characteristics. Firstly, because of its potentially great time resolution, it can act as both the effector and the detector for dynamical processes on timescales as short as 10 - s. Secondly, due to its spectral resolution and brightness, the laser can be used to prepare large amounts of a selected quantum state of a molecule so that the chemical reactivity or other dynamical properties of that state may be studied. Finally, because of its coherence as a light source the laser may be used to create in an ensemble of molecules a coherent superposition of states wherein the phase relationships of the molecular and electronic motions are specified. The dynamics of the dephasing of the molecular ensemble may subsequently be determined. 

Ensembles of molecules Molecular dynamics and Monte Carlo... 

The underlying concept of free-volume theory is that the movement of the molecules is intrinsically conditioned to the amount of free volume in a molecular ensemble the less the unoccupied space, the more the collisions among the molecules, which results in a slow response to a perturbation in an equilibrium state [115]. 

Femtosecond pulse trains offer another control knob to rotational excitation of molecules, namely, the control of its directionality. By applying a series of laser pulses, linearly polarized at an angle with respect to one another, either clockwise or counterclockwise rotation can be initiated in a molecular ensemble [27]. The effect has been experimentally demonstrated with a sequence of only two pulses [28], and longer pulse trains [29, 30]. The latter were dubbed chiral because of the directional rotation of light polarization from pulse to pulse shown in Figure 10.3a. Chiral pulse trains enable control of the sense of molecular rotation... 

In extending the studies of vibrational coherence to rotational coherence in isolated molecules, we formulated the concept of rotational recurrences (echoes ), which led to rotational coherence spectroscopy. A polarized picosecond (and later femtosecond) pulse was used to orient a molecular ensemble (Fig. 7). The molecules then rotate freely with different speeds... 

In order to determine specific phase regions of a molecular ensemble, we express the full energy of a linear molecule as a function of a polar coordinate 0 and of two angular velocities ... 

Chemical interference is mostly realized by selecting reactions capable of organizational interaction. Hence, an ensemble of molecules and, consequently, an ensemble of reactions, create an algorithm for implementation of interrelated spontaneous reactions able to interfere. Note that the structure of the molecular ensemble may be different, which may also affect the course of conjugated processes. The communication channels between self-organized systems (ensembles) of reactions are performed by reactive intermediate particles, general to all current processes. 

Each structural model must be chosen so as to match a particular set of observations. That is, the symmetry of the model of a molecule or of a molecular ensemble depends on the conditions of the relevant physical (or chemical) measurement, and may vary for the same system according to time scale of observation and instrumental sensitivity. Hence, whether the model of a chemical system is chiral or achiral depends on the conditions of observation. In what... 

If excitation takes place by intensive light, then, naturally, there may emerge in the molecular ensemble polarization moments of rank higher than 2. This may take place both in excited and in ground states. In this case the set Pq of odd rank characterizes orientation, whilst that of even rank characterizes alignment of the angular momenta of the molecules. 

Generally, dielectrics differ from conductors because they have no charges to move freely. However, a small displacement (compared to atomic dimensions) of electrons in their parent molecules may occur when this dielectric is embedded in an electric field. This effect is called the polarization, and a polarized dielectric will create its own field that can be compared with an external field imposed. We have also to note that if the dielectric molecules possess a permanent dipole moment, the orientational polarization takes place, revealing an average (over the molecular ensemble), nonzero dipole moment. As a consequence, the polarization field may alter the net, outer field significantly. 

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