Excitation inter-molecular

It should be mentioned that most of the analysis methods quoted above are generally only applied at the SCF or DFT level. This is certainly a severe limitation, in particular whenever Van der Waals interactions or other correlation effects play an important role. However, it is generally quite easy to decompose correlation energies into different physical contributions, for instance by analyzing the effect of different types of excitations Inter-molecular double excitations are mainly responsible for Van der Waals interactions, intra-molecular doubles for the improvement of the SCF wave functions or densities of the fragments. 

Conventional spontaneous Raman scattering is the oldest and most widely used of the Raman based spectroscopic methods. It has served as a standard teclmique for the study of molecular vibrational and rotational levels in gases, and for both intra- and inter-molecular excitations in liquids and solids. (For example, a high resolution study of the vibrons and phonons at low temperatures in crystalline benzene has just appeared [38].)... 

Figure B2.5.18 compares this inter molecular selectivity with intra molecular or mode selectivity. In an IR plus UV, two-photon process, it is possible to break either of the two bonds selectively in the same ITOD molecule. Depending on whether the OFI or the OD stretching vibration is excited, the products are either IT -t OD or FIO + D [24]- hr large molecules, mirmnolecular selectivity competes with fast miramolecular (i.e. unimolecular) vibrational energy redistribution (IVR) processes, which destroy the selectivity. In laser experiments with D-difluorobutane [82], it was estimated that, in spite of frequency selective excitation of the...

From the results of the fluorescence spectroscopic study it is concluded that excitation energy at the lowest excited state of a PDA derivative having a thioester moiety is localized at the thioester group intra- or inter-molecular energy transfer from the conjugated system of the PDA to the thioester moiety must have occurred in the crystalline state to afford a photostable crystal (Hasegawa et al., unpublished data). 

Electrons of still lower energy have been called subvibrational (Mozumder and Magee, 1967). These electrons are hot (epithermal) and must still lose energy to become thermal with energy (3/2)kBT — 0.0375 eV at T = 300 K. Subvibrational electrons are characterized not by forbiddenness of intramolecular vibrational excitation, but by their low cross section. Three avenues of energy loss of subvibrational electrons have been considered (1) elastic collision, (2) excitation of rotation (free or hindered), and (3) excitation of inter-molecular vibration (including, in crystals, lattice vibrations). 

In the following scheme the difference between intra- and inter-molecular electronic excitation energy transfer is summarized (as formulated in 2>) ... 

Despite the difficulty cited, the study of the vibrational spectrum of a liquid is useful to the extent that it is possible to separate intramolecular and inter-molecular modes of motion. It is now well established that the presence of disorder in a system can lead to localization of vibrational modes 28-34>, and that this localization is more pronounced the higher the vibrational frequency. It is also well established that there are low frequency coherent (phonon-like) excitations in a disordered material 35,36) These excitations are, however, heavily damped by virtue of the structural irregularities and the coupling between single molecule diffusive motion and collective motion of groups of atoms. 

In the present work the Cl procedure ( ) employed includes single, double, and higher excited configurations, and can treat in a natural way, using the localized monomer basis orbitals, intra- as well as inter-molecular excitations. States which arise from such monomer-based excitations can then be interpreted in terms of their locally-excited, excitonic, CT, or "mixed" character. Details as to the nature of the dimer states have been discussed in our earlier works (7, 8). 

In (1), Hq yields the total energy of system in which the molecules and the lattice are excited, yet there are no interactions between molecules and the lattice. The transfer of an electron from site m to site n is given by //j. Polaronic effects, i.e., effects due to the interaction of the electronic excitation and the lattice, are given by H2 and H. hi H2, the energy of the site is reduced by the interaction with the lattice vibration. In H, the lattice vibration alters the transition probability amplitude from site m to n. The term lattice vibration may refer to inter-molecular or intra-molecular vibrations. Static disorder effects are considered in H4, which describes the changes to the site energy or transition probabihty amplitude by variations in the structure of the molecular sohd. 

In conclusion, we have found that the intramolecular dynamics in the benzene molecule at low excess energy is not strongly influenced by the additional three vibrational degrees of freedom of the benzene-Ar complex. The coupling of the excited intramolecular modes to the low-frequency inter-molecular modes is weak. The observed 40% decrease of the lifetime of the 61 state does not depend on the individual excited rotation and points to an external heavy-atom effect as the source of the lifetime shortening observed for the same selectively excited rovibronic state. 

Photolysis. Photolysis of a chemical can proceed either by direct absorption of light (direct photolysis) or by reaction with another chemical species that has been produced or excited by light (indirect photolysis). In either case photochemical transformations such as bond cleavage, isomerization, intramolecular rearrangement, and various inter-molecular reactions can result. Photolysis can take place wherever sufficient light energy exists, including the atmosphere (in the gas phase and in aerosols and fog/cloud droplets), surface waters (in the dissolved phase or at the particle-water interface), and in the terrestrial environment (on plant and soil/mineral surfaces). 

An electronic excited state of a metal complex is both a stronger reductant and oxidant than the ground state. Therefore, complexes with relatively long-lived excited states can participate in inter-molecular electron transfer reactions that are uphill for the corresponding ground state species. Such excited state electron transfer reactions often play key roles in multistep schemes for the conversion of light to chemical energy ( 1). 

In Eq. (4), one can see that there are two terms that depend on the space-phase factor. Eq. (5) clearly shows this situation coherence is generated between the two molecules. This coherent excitation can be called as inter-molecular coherence. This type of coherent excitation can be seen in femtosecond pump-probe non-linear coherent optical scattering spectroscopy. This chapter shall only focus on ultrafast radiationless transition as well as the dynamics of the intramolecular coherence and its relaxation. 

FRET occurs when the electronic excitation energy of a donor chromophore is transferred to an acceptor molecule nearby via a through-space dipole-dipole interaction between the donor-acceptor pair.80 The strong dependence of the FRET efficiency on donor-acceptor distance has been widely exploited in studying the structure and dynamics of proteins and nucleic acids, in the detection and visualization of inter-molecular association, and in the development of intermolecular binding assays.81,82... 

The reader should notice that in this chapter only thermochemical reactions have been considered. A completely different situation is expected with photochemical reactions because of the excited states involved. The solvent model included in the MCSCF code of GAMESS package can work with excited states, but it is important to remark that the model in this case is incomplete and needs substantial improvements. The inter-molecular interactions, when one of the molecules is in an excited state, are not yet fully understood and solute-solvent interactions in this case must account for complicated charge transfer and resonance effects. 

These intra- and inter-molecular deprotonations of the cation radical readily occur, so that the cation radical is unstable even at 4 K. The direct scission of a C-H bond in the excited state PMMA cannot be excluded as an additional source of either of the main-chain radical or the side-chain radical. The H atom generated from the excited state PMMA or from the recombination of a proton with an electron will recombine with the polymer radical or abstract an hydrogen to generate also the main-chain or the side-chain radical as... 

The V-B coupling Hamiltonian to first order in the three HOD dimensionless normal coordinates is Hv b = —2, c], l , where F, is the inter-molecular force due to the solvent exerted on the harmonic normal coordinate, evaluated at the equilibrium position of the latter. This force obviously depends on the relative separations of all molecules, and on their relative orientations. In the most rigorous quantum description of rotations, this term would depend on the excited molecule rotational eigenstates and of the solvent molecules. Instead rotation was treated classically, a reasonable approximation for water at room temperature. With this form for the coupling, the formal conversion of the Golden Rule formula into a rate expression follows along the lines developed by Oxtoby (2,53), with a slight variation to maintain the explicit time dependence of the vibrational coordinates (57),... 

The singlet triplet energy gap, A/isx. in organic biradicals35 182 183 and (inter-molecular) radical ion pairs184-190 has been shown to be a useful indicator of electronic coupling in ET and excitation energy transfer (EET) processes.191-194... 

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