Picosecond-studies

How can such problems be counterbalanced Since a large capacitance of a semiconductor/electrolyte junction will not negatively affect the PMC transient measurement, a large area electrode (nanostructured materials) should be selected to decrease the effective excess charge carrier concentration (excess carriers per surface area) in the interface. PMC transient measurements have been performed at a sensitized nanostructured Ti02 liquidjunction solar cell.40 With a 10-ns laser pulse excitation, only the slow decay processes can be studied. The very fast rise time cannot be resolved, but this should be the aim of picosecond studies. Such experiments are being prepared in our laboratory, but using nanostructured... 

Early picosecond studies were carried out by Schneider et al, [63] on the parent spiro-oxazine (NOSH in Scheme 8) and similar derivatives. In a back-to-back work, they also described a complimentary CARS (coherent anti-Stokes Raman spectroscopy) investigation [69], Simply put, these authors found that the closed spiro-oxazine ring opened in 2-12 psec after laser excitation. The reaction was slower in more viscous solvents. An intermediate state formed within the excitation pulse and preceded the formation of merocyanine forms. This transient was named X in deference to the X transient named by Heiligman-Rim et al. for the spiropyran primary photoproduct [8], (See also the previous section.) The name X has since been adopted by other workers for the spiro-oxazines [26,65],... 

G. W. Hoffman, T. J. Chuang, and K. B. Eisenthal, Picosecond studies of the cage effect and coUision induced predissociation of iodine in liquids. Chem. Phys. Lett. 25(2), 201-205 (1974). 

As has been shown by time-resolved flash photolysis measurements in colloidal titanium dioxide suspensions trapping is a very fast process. Rothenberger et al. performed picosecond and nanosecond transient absorption experiments on titanium dioxide and observed that the electron trapping time was faster than 30 ps, the time resolution of their laser system [4e]. The trapping time for holes was estimated to be < 250 ns. In a recent picosecond study by Serpone et al. on titanium dioxide colloids solutions of varying diameters it was observed that the spectra of trapped electrons as well as of trapped holes are fully developed after a laser... 

Heilweil EJ, Casassa MP, Cavanagh RR, Stephenson JC. Picosecond studies of vibrational energy transfer in surface adsorbates. Ann Rev Phys Chem 1989 40 143-171. 

Picosecond study of pyrazine seeded in supersonic 271 expansions of He. Decay behaviour interpreted in terms of rapid dephasing of initially populated singlet state Decays of rotational states of the (0-0) transition 310 of pyrazine. When Fourier transformed, beating decays are obtained... 

The lifetime of the charge-transfer state, [P700 Ao ], is expected to be extremely short and the time required to form this state shorter yet. Thus attempts to use picosecond spectroscopy to examine the behavior of Aq were made soon after the studies described above were reported. Following the earlier picosecond studies in 1979, additional studies began to provide not only more detailed but considerably improved spectral and kinetic information about the primary acceptor Aq. In this section, we will summarize the results of these picosecond studies in approximate chronological order. 

Initial picosecond studies were reported by Fenton, Pellin, Govindjee and Kaufmann of Urbana and by Shuv ov, Ke and Dolan of Yellow Springs. Fenton et al. used a PS-I particle fractionated from spinach thylakoids and S-ps, 528-nm pulses for excitation. They measured the kinetics of the absorbance increase near 800 nm and confirmed that P700 was photooxidized within 10 ps of the excitation flash. The authors also suggested that a reduced electron acceptor absorbing at 700 and 730 nm was formed always within lOp and was then reoxidized in tens of picoseconds. 

Picosecond Studies of Proton Tranter in Cyclodextrin Complexes 225... 

Picosecond Studies of Proton Transfer in Cyclodextrin Complexes... 

We conclude this section by stating that even though hydrodynamic behavior during electron solvation in pure liquids is observed, it does indeed mask the microscopic details of the solvation mechanism, although to no greater extent than is now realized in picosecond studies of the orientational dynamics of more classical molecules. 

The first picosecond study on a biological molecule was centered on the kinetics of the primary intermediate, bathorhodopsin during the visual transduction process. Low-temperature experiments had established the presence of an intermediate species referred to as bathorhodopsin, which seemed to be quite stable at low temperatures, 77 K and 7 K. However, because of its ultrafast formation time constant at room temperature, it could not be measured before the development of picosecond spectroscopy. It was established however that the first intermediate bathorhodopsin decayed, at room temperature, into a second intermediate lumirhodopsin then to two other species called metarhodopsin I and metarhodopsin II. Eventually, at some point, the chromophore isomerizes. " The intermediate at which the isomerization occurs is not known or at least unequivocally agreed upon. The recent picosecond... 

The first picosecond studies on rhodopsin and possibly of any biological system were performed by Busch et al.," who studied the kinetics of the first photoinduced intermediate of rhodopsin, bathorhodopsin at room... 

M. Berg, A. L. Harris, and C. B. Harris, Phys. Rev. Lett., 54, 951 (1985). Rapid Solvent-induced Recombination and Slow Energy Relaxation in a Simple Chemical Reaction Picosecond Studies of Iodine Photodissociation in CCI4. 

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