Bright state

Contrast. This can be quantified as the ratio of transmitted light intensity in the bright state compared to the dar... 

Fig. 16. Twisted nematic LCD showiag the V dark state (right), where D is the threshold voltage of the ceU.

Hare PM, Crespo-Hernandez CE, Kohler B (2006) Solvent-dependent photophysics of 1-cyclohexyluracil ultrafast branching in the initial bright state leads nonradiatively to the electronic ground state and a long-lived 1 nit1 state. J Phys Chem B 110 18641... 

The excited vibrational states can be considered as quasi-eigenstates [41]. As can be seen in the simplified scheme of Figure 2.2, these states are a result of the relatively strong coupling between a zero-order bright state (ZOBS), namely i >, with several zero-order dark states (ZODS), l > [48], that are further weakly coupled to the bath states that include a dense manifold of nearly equally coupled levels with a finite decay rate. 

Fig. 2. Pump and probe scheme within a tiers picture (schematic). The zeroth order bright state which is not Franck-Condon (FC) active in the electronic transition is excited via the near IR- laser pulse. FC-active modes m later tiers having no population at t=0 are probed and their time dependent population is a measure for IVR (Vj being matrix elements connecting zeroth order states) in the molecule giving rise to an enhancement of the electronic absorption.

One explanation is that the radiative transition probabilities of the excimers are similar to those of the monomeric singlet states, but the excimers are formed in much lower yields. This could be the case if the initially excited state (the optically bright state populated by absorption) forms the excimer state in competition with other decay channels. An alternative explanation is that the excimer states are formed in high yield, but have low radiative transition probabilities (i.e. they are relatively dark in emission). 

Figure 11. Comparison between the expectation values of several observables pertaining to the state of the linear HCCH molecule at the end of the pulse for various transform-limited pulses. A 91-state active bright-state basis approximation is compared with the result of a full calculation (labeled DVR).

Long progressions of feature states in the two Franck-Condon active vibrational modes (CC stretch and /rani-bend) contain information about wavepacket dynamics in a two dimensional configuration space. Each feature state actually corresponds to a polyad, which is specified by three approximately conserved vibrational quantum numbers (the polyad quantum numbers nslretch, "resonance, and /total, [ r, res,fl)> and every symmetry accessible polyad is initially illuminated by exactly one a priori known Franck-Condon bright state. 

The finer structure within each feature state corresponds to the dynamics of the Franck-Condon bright state within a four-dimensional state space. This dynamics in state space is controlled by the set of all known anharmonic resonances. The state space is four dimensional because, of the seven vibrational degrees of freedom of a linear four-atom molecule, three are described by approximately conserved constants of motion (the polyad quantum numbers) thus 7-3 = 4. 

In a sense, the dynamics depicted in Fig. la are almost indescribably complex. The complexity reflects the presence of the N(N-1)/2 beat frequencies that arise from N eigenstates in a polyad. However, several crucial qualitative features are evident. The ZOBS has P(0) = 1 and all of the dark states have P(0) = 0. For the bright state P(t) oscillates about -0.8 with a peak-to-peak amplitude of -0.4 and a shortest dominant period of -200 fs (although the oscillation contains at least two dominant Fourier components). For one of the dark states P(t) oscillates about -0.15 with a peak-to-peak amplitude of -0.30 and a period of -200 fs (also containing at least two Fourier components). Thus (0, 1, 0, 6+2, 2 2)0 is the dominant partner of the ZOBS. Most of the 0.1 oscillatory probability not accounted for by the (0, 1, 0, 8°, 0°)°, (0, 1, 0, 6+2, 2 2)0 pair is found in the (0, 1, 0, 6°, 2°)° dark state but with a period of -400 fs. The remote dark state shows a very small, spiky P(f), with a stochastic appearance. 

The bright-state character corresponding to localized vibration of the AB bond equals cs 2. For anaharmonic molecules it is not uncommon to find eigenstates with large local mode character, i.e., with cs 2 = 1. 

First, we consider a schematic example to illustrate how the cation electronic structures can be used in (angle integrated) TRPES to disentangle electronic from vibrational dynamics in ultrafast nonadiabatic processes, depicted in Fig. 2. A zeroth- order bright state, a, is coherently prepared with a femtosecond pump pulse. According to the Koopmans picture [13, 41, 42], it should ionize into the a+ continuum, the electronic state of the cation obtained upon removal of the outermost valence electron (here chosen to be... 

Figure 8. Time-resolved photoelectron spectra revealing vibrational and electronic dynamics during internal conversion in DT. (a) Level scheme in DT for one-photon probe ionization. The pump laser prepares the optically bright state S2. Due to ultrafast internal conversion, this state converts to the lower lying state Si with 0.7 eV of vibrational energy. The expected ionization propensity rules are shown S2 —> Do + e (ei) and Si —> D + (b) Femtosecond time-...

Franck-Condon dissociative continuum. At long times (Af = 3500 fs), a sharp photoelectron spectrum of the free NO(A, 3,v) product is seen. The 10.08 eV band shows the decay of the (NO)2 excited state. The 9.66 eV band shows both the decay of (NO)2 and the growth of free NO(A, 3,v) product. It is not possible to fit these via single exponential kinetics. However, these 2D data are fit very accurately at all photoelectron energies and all time delays simultaneously by a two-step sequential model, implying that an initial bright state (NO)2 evolves to an intermediate configuration (NO)2f, which itself subsequently decays to yield free NO(A, 3s) products [138]... 

Whenever the lowest (TVth) order perturbation theory for the IV-photon problem i j valid, it is possible to generate a wave packet of bright states, assuming that suc r bright states exist. To see this, partition the excited state manifold into bright states s) and dark states %m). The eigenstates E ) of the molecular Hamiltonian HM can therefore be written as. ... 

Having shown that it is possible to prepare bright states, or to prepare specific ( vibrational states in particular cases, we consider the utility of such states. If the task is merely to control the populations of stable molecules, then the discussion above demonstrates the possibility of doing so. Similarly, for example, Rabitz et al. [110, 318] have shown that it is possible to control the vibrational states of local g -bonds in a chain of harmonic oscillators. 

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