Transition dipole moment direction

Rosell FI, Boxer SG (2003) Polarized absorption spectra of green fluorescent protein single crystals Transition dipole moment directions. Biochemistry 42 177-183... 

Benko et al, 2004). Furthermore, anisotropy of the absorption signal can also be used to differentiate these species, as they often have different transition-dipole moment directions (Martini et al, 1998). Shown in Fig. 11.3 is an example of a careful transient absorption study of NS/TiOa (Benko et al, 2002 KaUioinen et al, 2002). By measuring the transient spectral evolution of the reactant (adsorbate excited states) and products (cation and injected electrons) over the visible and near-IR range, the injection kinetics (shown in the inset) were unambiguously determined. 

Let us consider molecule X in Fig. 1, located in domain , with a transition dipole moment of —27° relative to the b -sods. Molecule Y located in domain has an orientation of -1-27°. Both molecules have the same environment and therefore belong to the same optical site. However their transition dipole moment direction is different. If both domains are present in the probing volume a histogram of the distribution of the Q, values has two peaks symmetrically arranged relative to 0° (see [1]). If only one domain is present, just one peak is observed. 

The polarization and orientation dependence of plasmon coupling described above is very similar to absorption spectra shifts observed in organic molecules upon their dimerization or aggregation. Organic chromophores dimerized head-to-tail with respect to their transition dipole moment direction (known as J-dimers) show an absorption band that is red-shifted compared to that of the isolated... 

Computed excitation energies Af (eV) at CASPT2 level, oscillator strengths f, dipole moments p(0), dipole moment directions ir(deg), and transition dipole moment directions TDMdir(deg) for the low-lying electronic transitions of psoralen... 

It turns out that there is another branch of mathematics, closely related to tire calculus of variations, although historically the two fields grew up somewhat separately, known as optimal control theory (OCT). Although the boundary between these two fields is somewhat blurred, in practice one may view optimal control theory as the application of the calculus of variations to problems with differential equation constraints. OCT is used in chemical, electrical, and aeronautical engineering where the differential equation constraints may be chemical kinetic equations, electrical circuit equations, the Navier-Stokes equations for air flow, or Newton s equations. In our case, the differential equation constraint is the TDSE in the presence of the control, which is the electric field interacting with the dipole (pemianent or transition dipole moment) of the molecule [53, 54, 55 and 56]. From the point of view of control theory, this application presents many new features relative to conventional applications perhaps most interesting mathematically is the admission of a complex state variable and a complex control conceptually, the application of control teclmiques to steer the microscopic equations of motion is both a novel and potentially very important new direction. 

The PPP-MO method is capable of calculating not only the magnitude of the dipole moment change on excitation, but it can also predict the direction of the electron transfer. The vector quantity that expresses the magnitude and direction of the electronic transition is referred to as the transition dipole moment. For example, the direction of the transition dipole moment of azo dye 15f as calculated by the PPP-MO method is illustrated in Figure 2.15. 

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. 

Use of plane polarized light. The intensity of a spectral transition is directly related to the transition dipole moment (or simply the transition moment), a vector quantity that depends upon the dipole moments of the ground and excited states. For aromatic ring systems, the transition dipole moments of the ji-n transitions lie in the plane of the ring. However, both the directions and intensities for different n-n transitions within a molecule vary. 

The retinal Schiff base chromophore is embedded in rhodopsin with its transition dipole moment parallel to the plane of the discs, i.e., perpendicular to the direction of travel of the incoming photons. Absorption of a photon leads to a sequence of readily detectable spectral changes.37,46113,499,500 The relaxation times indicated in Eq. 23-37 are for 20°C. 

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