Ground-state dynamics, bimolecular

The rate of absorption (step i) can be expressed as the absorption intensity /abs (which depends on the concentration of the ground-state complex and the intensity of light used in excitation), while the rate of luminescence (step ii) and the rate of all the nonradiative decay paths (step iii) follow first-order rate laws that depend only on the concentration of the excited-state complex (nonradiative collisional quenching by solvent is not unimolecular, but follows first-order kinetics because of the large excess of solvent molecules). Dynamic quenching (step iv) results from an electron-transfer reaction during a collision between a quencher molecule and an excited-state complex. This bimolecular reaction has a... 

The reaction dynamics of few excited complexes are known however, the opportunities provided by pulsed lasers promise to make this research area one of major emphasis of mechanistic studies. Such methods are necessary because few transition-metal complexes exist as electronically excited states in RT solutions with lifetimes exceeding 1 fjis, and many are shorter lived. Several competing processes lead to ES decay nonra-diative deactivation to the ground state (GS), radiative deactivation (i.e., emission) to the GS, unimolecular reaction to products (such as ligand substitutions or redox decomposition) or bimolecular electron transfer or energy transfer with another species, Q, in solution. These processes are indicated in Eqs. (a)-(e) for a hypothetical complex [MLJ" + ... 

Among four-atom reactions this system has become a prototype test case for the comparison between quantum state resolved dynamics experiments and bimolecular collision theory. In 1973 the first semi-empirical LEPS and BEBO PESs were constructed by Zellner and Smith [56]. The subsequent development of a global H-HOH(A ground state PES in 1980 [20b], based on ab initio calculations [20ak was favoured by the fact that three of the four atoms involved are H atoms. The... 

Changes in the electronic and molecular structures of a molecule A due to a transition from its ground to an excited state can result in creation of conditions for chemical bonding between the excited molecule A (in the whole review the symbol A will denote an excited particle A in general the number X in the symbol XA denotes the multiplicity of the excited particle A), and another molecule Q of the system, giving rise to an excited adduct (A — Q) [1], Such an adduct formed in a bimolecular dynamic adiabatic process... 

Probing product state distributions by multiphoton ionization is one of the most sensitive methods for the analysis of both bimolecular and photofragmentation dynamics. For example, by using REMPI one can measure the rotational state distribution in the N2 fragment produced in the photofragmentation of N2O it was found that the maximum in the rotational state population is near J 70. This reveals that although the ground electronic state is linear, the excited state is bent and thus the recoil from the O atom results in rotational excitation of the N2 molecule... 

The general understanding of molecular dynamics rests mainly upon classical mechanics this holds true for full bimolecular collisions (see Trajectory Simulations of Molecular Collisions Classical Treatment) as well as half-collisions, i.e., the dissociation of a parent molecule into different products. The classical picture of photodissociation closely resembles the time-dependent picture the electronic transition from the ground to the excited electronic state is assumed to take place instantaneously so that the internal coordinates (Qi) and corresponding momenta (/, ) of the parent molecule remain unchanged during the excitation step (vertical transition). After the molecule is promoted to the PES of the upper state it starts to move subject to the classical equations of motion (Hamilton s equations)... 

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