Transitions between excited states

The terms in the dipole operator that connect excited states are now N( and N. So, 

This is independent of chain iength, as shown in Fig. F.I for iarge chains. Notice that this matrix eiement connects states with the same vaiue of j and opposite particie-hoie parity. Thus, these transition dipoie moments are oniy nonzero when 

In the strong-coupling limit a general excited state is described by eqn (6.30) or eqn (6.31). However, now the basis state R + r/2,R — r/2) corresponds to an empty site at i - r/2 and a doubly occupied site at / - - r/2 in a sea of singly occupied sites, as described in Section 6.3. 

---

FIGURE 7.4 Modified Jablonski diagram showing transitions between excited states and the ground state. Radiative processes are shown by straight lines, radiationless processes by wavy lines. IC = internal conversion ISC = intersystem crossing, vc = vibrational cascade hvf = fluorescence hVp = phosphorescence. 

The emission spectrum of the cathode material includes a number of intense, sharp lines arising from transitions between excited states and the ground state, so-called resonance radiation. Generally, only a few resonance lines per element are suitable for quantitative work and there will be variation in the ranges of concentration over which absorbance measurements... 

Fig. 12.2. A schematic representation of several transitions between excited states leading to photochemical reaction products.

Because Tx contains the host information, once a set of three Tx parameters has been obtained by absorption spectroscopy, it can be used to calculate probabilities for aity other transition between excited states of the same ion (Auzel 1969b), provided matrix elements are known. Since these matrix elements involve free-ion states, they do not vary much from host to host and once calculated for one host they can be used expediently for others. Calculation of probabilities between excited states provides a convenient way to obtain the branching ratios (/3) of transitions... 

Modified Jablonski diagram showing transitions between excited states... 

Vall6sJ.A., Lazaro J.A., Rebolledo M. A. Analysis of competing mechanisms in transitions between excited states in Er-doped integrated Waveguides. IEEE J.Quantum. Electron. 2002 38 318-323... 

In the heaviest nuclei transitions between excited states are dominated by internal conversion electron emission over gamma emission. It is important to realize that the emission of conversion electrons is a direct process, and does not proceed via an intermediate gamma ray. This is mainly due to the increased probability of finding an atomic electron (its wave function) inside the nucleus where energy can be transferred to it directly. We define the internal conversion coefficient a as the ratio of the number of electrons that get emitted to the number of gamma rays emitted during the decay of a sufficiently large ensemble ... 

The width of the dip at the center of the Doppler amplification line is equal to the homogeneous linewidth 2F which may be considerably smaller than Aud. This fact has opened up strong possibilities for spectroscopy within the Doppler profile. Such a method has been used in experiments on measuring collisional broadening and isotope shifts and on stabilizing the laser frequency at the center of the amplification line. However, the spectral resolution in these experiments was limited by the homogeneous width 2/hom of the amplified spectral transition between excited states, which was relatively large. 

The large population density Nj which can be achieved in selectively excited levels E by optical pumping with lasers allows one to perform high-resolution spectroscopy of excited molecules with sufficient sensitivity. Many of the techniques applicable to molecules in their ground states (e.g., absorption spectroscopy, optical pumping, LIF, microwave spectroscopy) can be now transferred to transitions between excited states. In the following sections we briefly discuss some of these methods. 

The charge exchange collisions may result in highly excited states of the neutral species. Often the population of these excited states accumulates in metastable states with long lifetimes. This opens the possibility of performing laser spectroscopy on transitions between excited states. 

While the resonance lines, corresponding to transitions from the ground state, are for most atoms in the ultraviolet region, the transitions between excited states are generally in the visible to infrared range and are therefore more readily accessible to the tuning range of dye lasers. 

---