Quantum of excitation

C. Resonance energy transfer. The excitation energy can be transferred by resonance energy transfer, a radiationless process, to a neighboring molecule if their energy level difference corresponds to the quantum of excitation energy. In this process, the quantum, or so-called exciton, is transferred. 

Raman Spectroscopy The time-dependent picture of Raman spectroscopy is similar to that of electronic spectroscopy (6). Again the initial wavepacket propagates on the upper excited electronic state potential surface. However, the quantity of interest is the overlap of the time-dependent wavepacket with the final Raman state 4>f, i.e. < f (t)>. Here iff corresponds to the vibrational wavefunction with one quantum of excitation. The Raman scattering amplitude in the frequency domain is the half Fourier transform of the overlap in the frequency domain,... 

The concept of quantum yield is also extensively used to characterize the various photophysical processes. A complete account of this matter may be found in the recent book by Birks (13). The "phosphorescence quantum yield" is defined there as "the ratio of the number of phosphorescence photons emitted to the number of absorbed photons." In the same book, the name "phosphorescence quantum efficiency" is given to the fraction of the molecules in the triplet state which phosphoresce. This last quantity, however, does not depend on the number of quanta absorbed, and thus the word "quantum" is inappropriate. On the other hand, the term "triplet formation efficiency" used by Parker (14) to indicate the "number of triplet molecules formed per quantum of exciting... 

When a quantum of excitation reaches the RC, the primary donor P is excited to a new state P in which it is a powerful reducing agent. P transfers an electron to the initial acceptor I. To prevent the electron from falling back to P , the secondary acceptor X takes the electron from I and stabilizes the charge separation. To further stabilize this separation the secondary donor D gives an electron to P". ... 

This prescription maps the Hilbert space spanned by the original n diabatic states into one coinciding with a subspace of n-oscillators of unit mass and at most one quantum of excitation in a single specific oscillator. 

Davydov splitting for exciton resonance in anthracene, and for the first time obtained reasonable agreement with available experimental data. He used a dipole approximation for the intermolecular interaction and the only ingredients in his theory were the resonance frequencies and oscillator strength. In contrast to quantum theory described in this chapter the classical dipole theory does not take into account the contribution of the nondipole interaction, which are important in the majority of solids. It is clear that also multiexciton states including states with few quantum of excitations on the same molecule (what is forbidden for the two-level model) in classical harmonic oscillator theory contribute to the energy of excitons. However, in the framework of the classical theory it is impossible to develop the estimation of corrections which we discussed here. 

The I0,1> vibrational state with one quantum of excitation in the O-D mode is 2727 cm- higher than the 10,0> level and comes in resonance with the excited surface at lower UV frequencies. Hence, the dissociation in both the 0-H and O-D modes picks up at frequencies lower than that for the I0,0> level. The I0,1> state has larger O-D stretch, with the probability density peaking in the H-0 + D channel. The natural preference for H + O-D dissociation therefore is reversed and the H-0 + D flux is much more than the H + O-D flux in a broad range of frequencies. At higher... 

The two-color fleld employed here for selective dissociation of the 0-D bond and its power spectrum is shown in Figure 7.18a. The beat structure of the resulting pulse displays a frequency of 2752 cm which resonates with the vibrational frequency of the I0,1> state with one quantum of excitation in the 0-D mode (2727 cm i) and is nearly half of the vibrational frequency for the I0,2> state (5369 cm i). Moreover, the combinational U V frequency of this 50-fs two-color pulse is 55 160 cm (lower... 

Using I0,1> as the initial state with one quantum of excitation in the O-D mode, we find that favored dissociation of the O-H bond is reversed for a large range of photolysis frequencies, and H-O + D flux predominates over the H + O-D flux. Starting with I0,2> as the initial state with two quanta of excitation in the O-D mode, there is dominant dissociation of the O-D bond for a large interval of frequencies. 

---