Pump and Probe Experiments

Keszei, E., Murphrey, T. H. and Rossky, P. J. Electron hydration dynamics simulation results compared to pump and probe experiments, J.Phys.Chem., 99 (1995), 22-28... 

For the pump and probe experiments, the transmission T of a sample is defined in a very simple way, neglecting the reflectivity losses described in Sect. 2.1 ... 

A variety of processes and their mechanisms are now being clocked using femtosecond pump and probe experiments. It includes catalysis (to probe mechanism end improve catalysts), liquid phase reactions (to understand reactions in solution), polymers (to improve physical properties of polymers), and biological processes (e.g., to understand the primary photochemical step in vision). 

Barrier 1 is caused by the unfolding of the 23 aa long N-terminal linker of TK and at barrier 2 the autoregulatory tail is removed so that the ATP binding site is opened as seen in the pump-and-probe experiment (Fig. 15.4). If ATP binds, it mainly interacts with LYS36 (as seen in the experiment) and with MET34, and thus causes the additional energy barrier. 

Gratzel and coworkers have used a ruthenium (II) complex linked to Ti02 by means of a Ais-carboxylato-bipyridine ligand to construct an efficient photocell.Many details of the functioning of this photocell are not well understood, but it is based on efficient photo-induced injection of electrons, from the MLCT excited state, into the semiconductor. Femtosecond pump and probe experiments have demonstrated that at least some of the photoelectrons are injected within 50 ps of the MLCT excitation.This is one of the fastest electron-transfer rates yet measured it apparently occurs in competition with vibrational relaxation of the excited state. 

Evidence of positive optical gain is observed in Tm -Yb codoped oxyfluoride glass ceramic in an upconversion pump and probe experiment. The G4 level of the Tm ions is populated by an upconversion mechanism under excitation of the Yb ions at 975 nm with high power pulsed laser and give rise to an intense emission from the G4 to the F4 levels. The G4 — T4 electronic transition is stimulated with a low signal at 650 nm as a probe. 

In this context we are investigating the optical amplification properties of trivalent lanthanide ions doped into the oxyfluoride glass ceramics, with the purpose of extending the knowledge and the application perspective of this material. In this paper we present the results of a series of pump and probe experiments carried out on oxyfluoride glass ceramics activated with Tm -Yb. ... 

Figure 1. PL (dots) and PLE spectra of CdSe/ZnS (300 K) quantum dots with 3.4 + 0.4 nm radius. For PLE spectra the luminescence was monitored at 1.984 eV (arrow a , dashed line) and 2.016 eV (arrow b , solid line). The energy of the exciting pulse (2.353 eV, used in the pump-and-probe experiment) is shown by thick arrow. The energies of lSv2(h)-lS(e), 1 Pj,2(h)l I (e), lP i/2(h)-lP(e) transitions, calculated using the results of [2] for QDs of 3.15 nm and 3.35 nm radius, are pointed by arrows (A1,A2,A3 for 3.35 nm and B1,B2,B3 for 3.15 nm).

Picosecond laser excitation ( pump and probe experiments) allowed us to determine lifetimes of the singlet excited states of these dyes in some cases [88c, 88e],... 

With femtosecond pump-and-probe experiments fast motion pictures of a vibrating molecule may be obtained, and the time behavior of the wave packets of coherently excited and superimposed molecular vibrations can be mapped. This is illustrated by the following examples dealing with the dynamics of molecular multiphoton ionization and fragmentation of Na2, and its dependence on the phase of the vibrational wave packet in the intermediate state [821]. There are two pathways for photoionization of cold Na2 molecules in a supersonic beam (Fig. 6.100) ... 

In a femtosecond pump-and-probe experiment the pump pulse excites the vibrational levels v = 10-12 in the A X y state of Na2 coherently. The vibrational spacings are 109 cm and 108 cm . The probe laser pulse excites the molecules only from the inner turning point into a higher Rydberg state. If the fluorescence /pKAr) from this state is observed as function of the delay time At between the pump and probe pulses, calculate the period ATi of the oscillating signal and the period AT2 of its modulated envelope. 

Femtosecond pump and probe experiments allow for real-time measurements of the collision complex lifetime, as we have seen earlier. Suppose the AB CD complex is formed in a supersonic expansion. If the AB molecule undergoes photofragmentation along a preferred direction on photolysis leading to hot A atoms, then not only can the ACD complex lifetime be measured, but also the time evolution of the AC + D products formed in the bimolecular reaction. 

Wulff M, Plech A, Eybert L, Randier R, Schotte F, Anfinrud R 2003. The realisation of sub-nanosecond pump and probe experiments at the ESRF . Faraday Discuss. 122 13 26. 

In addition, short-pulse tunable optical parametric oscillators have been realized, where the pump wavelength and the signal or idler waves can be used for pump-and-probe experiments [11.128]. The wide tuning range allows more detailled investigations compared to the restricted use of fixed frequency lasers [11.129]. Another useful short-pulse source for these experiments is a three-wavelength Ti sapphire laser, where two of the wavelengths can be indepently tuned [11.130]. 

This dissociation-recombination system differs from the foregoing examples in that it involves polar molecules in aqueous solution, rather than low-polar or non-polar molecules in low-polar solvents. It has been studied by sub-picosecond pump-and-probe experiments. 

In order to monitor the real-time dynamics of gas molecules interacting with surface, time-resolved study is required. It is generally known that the time domains for the gas adsorption/desorption on surface are within pico-second regime while the molecular vibration on surface is within femto-second regime. To accommodate this time-requirement as well as chemical analysis on surface, a type of pump and probe experiment is required, which makes use of synchronization between a laser pulse and a synchrotron radiation pulse of AP-XPS endstation. For example, the carrier dynamics and reaction mechanism of photocatalysts under AP conditions can be an ideal system to look at with this time-resolved experimental set-up. At present, the synchronization technique has been well developed as shown in a block diagram (Fig. 9.24). This time-resolved set-up can be further refined and adapted into advanced system when the free electron X-ray source is available. 

Picosecond pump and probe experiments of PhOH-tJ Hj) [147,148] showed a distinct onset to ESPT reaction at n = 5 ammonia molecules, and the n = 5 and 6 clusters reacted in 55 and 65 ps, respectively. In a mixed solvent system Ph0H-(NH3)j(CH30H), the reaction rate decreased remarkably (750 ps), i.e., the substitution of a single CH3OH molecule for an NH3 molecule caused a substantial decrease in reaction rate. The reduced reactivity in the presence of a single CH OH molecule was explained by the unfavorable solvent structure for stabilizing a proton as compared to that of pure ammonia clusters [15],... 

Several combinations of pump and probe experiments are possible (i) UV-Vis pump/visible single wavelength probe, types of the data generated are absorption changes at a certain wavelength (ii) UV-Vis pump/white light probe, types of the data generated are time-resolved absorption spectra (Fig. 8.15). 

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