Hole-burning experiments

In some extremely iimovative recent experiments, Hochstrasser and co-workers [ ] have described IR transient hole-burning experiments focused on characterizing inliomogeneous broadening in the amide 1... 

Additional evidence for structural flexibility of small peptides on very fast time scales can be obtained from dynamical hole-burning experiments. An example is shown in Fig. 23, (30) which reflects a cut through the 2D... 

Incidentally, the photochromic compounds described in the last section cannot be used for photochemical hole-burning experiments. This is because the hole-burning experiment requires a level-selective transition in order to... 

There are only a few gas-phase experiments of the benzene dimer. Some experiments point to a T-shape dimer while others ° implicate a sandwich or more likely a displaced stracture. Hole-burning experiments find evidence for multiple different structures. The experimental estimates of the binding energy of 77 are 1.6 0.2 and 2.4 0.4 kcal mol ... 

Z- E isomerization yield is nearly temperature-independent (Figure 1.10) or increases at low temperature, with only a small difference for excitation to the two lowest-excited states. So obviously, the E —> Z photoisomerization— after irradiation to the (n,7C ) state as well as the Z —> E isomerization— proceeds even at low temperature and in frozen solvents. In solid matrices, fast and slowly isomerizing molecules are observed on it —> it excitation. The fast process has a quantum yield of < = 0.14 that is temperature independent down to 4 K. With strong lasers, photoisomerization in the E —> Z direction have been exploited, even at 4 K in hole burning experiments. Thus, azobenzene photoisomerization cannot be frozen out. 

Note that the 3-ps charge separation time is nearly the same as that found in the purple bacterial reaction centers (see Chapter 7) and also consistent with predictions from picosecond fluorescence measurements " as well as results from low-temperature hole-burning experiments. However, starting from 1992, a series of studies, mostly from the Imperial College of London groups , and from others , support a 21 time... 

A yet exotic experimental approach in exchange experiments are the so-called hole-burning experiments in which a part of the anisotropic line shape (i.e., a certain orientation of molecules) is selected by either selective excitation or saturation and the redistribution of spins into this orientation is observed during a mixing period that may exceed (see Chapter 7.2 of Ref. 140). This idea has found a few applications in systems with reasonably broad spectra like and (Fig. 15). ... 

Photon echo and optical hole burning experiments on ionic dyes... 

See also Section VII.B.) Expression (26) further shows that also in optical hole-burning experiments the triplet state forms a bottleneck in the optical pumping cycle and leads to an increased hole width. We finally note that from the observed hole-width as a function of saturation power not only optical T2 may be obtained but also the transition dipole. 

We finally note that computer analysis of the hole width as a function of burning power shows that the functional form of the power dependence of the photochemical hole is identical to the one obtained for steady-state hole-burning. This assures that an appropriate extrapolation procedure will enable us to determine the optical homogeneous lineshape from a photochemical hole-burning experiment. In the following section we will review the high-resolution photochemical hole-burning experiments that have been performed so far and emphasize the most important results obtained. 

Another type of hole-burning experiment on DMST was done whereby a vibronic transition was excited. In this case, as Fig. 9c shows, no hole was... 

Laser hole-burning experiments in the nanosecond time domain can reveal the picosecond time history of the relaxation times in an n-level system of the molecule if those relaxation times are fast (picosecond) compared to the duration of the laser saturating pulse (nanosecond). Under these circumstances, the levels of the system can be treated as photostationary states and the kinetic equations solved exphcitly for the rate constant between any two specified levels. This leisurely approach to picosecond phenomena is equally valid in the picosecond time domain. 

Similar dramatic effects of selective solvation have been also seen in the laser-induced electron transfer (LIFT) processes first discussed in Section V. More recent hole-burning experiments employing a Nd YAG laser indicate that laser saturation at 330 nm also produces a significant, and... 

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