Transition dipole moment, direct molecular

Active control of population transfer using the control relation displayed in Eq. (5.23) has been demonstrated experimentally by Sherer et al. [18]. In this experiment gaseous I2 was irradiated with two short (femtosecond) laser pulses the first pulse transfers population from the ground-state potential-energy surface to the excited-state potential-energy surface, thereby creating an instantaneous transition dipole moment. The instantaneous transition dipole moment is modulated by the molecular vibration on the excited-state surface. At the proper instant, when the instantaneous transition dipole moment expectation value is maximized, a second pulse is applied. The direction of population transfer is then controlled by changing the phase of the second pulse relative to that of the first pulse. 

The polarization measurements showed that the Cl atoms and SnCl fragments had the same anisotropy factor 3 = 0.21 0.01, which, if the dissociation is fast compared with molecular rotation, suggests that there is a angle of 46.5 0.4° between the transition dipole moment and the dissociation direction. 

Polarized absorption spectroscopy is a powerful diagnostic tool for investigating molecular structure and the symmetry considerations discussed above can be extended to the situation where the incident light is polarized along a particular direction. The strength of the interaction of the transition dipole moment, A(. -,k , with the electric vector of the... 

The comparison of the Mfiu values with those of Mabs allows one to obtain information about the changes in the electronic structure and molecular conformation between the Franck-Condon excited state initially reached upon excitation and the solvent-equilibrated fluorescent state [14]. Electronic transition dipole moments are mainly determined by the direct interactions between the lowest CT state and the ground state (So), and by the contributions from the locally excited configurations [14, 54, 56, 57]. For example, for the fluorescent CT state one can obtain... 

The transitional dipole moment operator M contained in Eq. 1 is a vector quantity, or in other words the change in poation of the electron in the transition is in a fixed direction with reject to some system of coordinates in which the molecular frame is fixed. Thus the dipole moment operator is resolvable in three directions such that... 

The exciton model of linear aggregates was used to explain the evolution of the electronic state parameters with stepwise incorporation of additional monomer units [64,408,409]. In this model, the transition dipole moments have only one component directed along the main molecular axis. Thus, the amplitude of the transition dipole moment is expressed by Eq. (47) for nc< 12. 

Since all but one of the electrons in the given molecule remain unchanged in state as a result of electronic excitation, then only the wavefunctions involved directly in the electronic transition need be considered in defining the transition dipole moment. In the case of biological macromolecules and macromolecular assemblies, relevant wavefunctions usually correlate to lone pair orbitals, n, and ttItt molecular orbitals such that only two main types of transition dipole moment need be considered, which are ( jl n ) and (tt /2 tt ) respectively. The first of these transition dipole moments is in fact zero, consequently corresponding jx electronic transitions are known as weak, symmetry forbidden transitions. The second of these transition dipole moments is always non-zero and consequently corresponding tt TT transitio ns are known as a stro ng, symmetry allowed transitions. The symmetry allowed transitions are at least 100 times more intense than symmetry forbidden transitions. 

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