Rate measurements pump-probe

Sitz G. O., Farrow R. L. Pump-probe measurements of state-to-state rotational energy transfer rates in N2 (v = 1), J. Chem. Phys. 93, 7883-93 (1990). 

Not only ionic evaporation has to be considered, but also excited state evaporation. Previous pump-probe experiments that conclude to the existence of ESPT show picosecond decays for one cluster size 1-4 and flat signals for larger ones [24]. For other authors, the decay is observed for the 1-3 complex [20]. Furthermore, the rate of the observed process is also typically the one of evaporation (of one ammonia molecule). In the non reactive Na(NH3)n system, evaporation rate has been measured and is also at the tens picoseconds order of magnitude[32]. It is clear that excited state evaporation must also be taken into account. 

Right Dependence of the dissociation rate constant kd on solvent composition. (A) data measured using the TCSPC technique, (o) data measured by the pump probe technique. 

An analysis of the time dependent transient photo-reflectance gives us a good estimate of the effective pair recombination rate [8], The inset in Fig. 1(b) shows the average reflectance change as a function of the delay between pump and probe pulses at 6 K. In accordance with other BCS superconductors the effective recombination time is found to be a few nanoseconds. One important remark is that, within the experimental time resolution, no evidence of multiple decays is found. In fact, ultra-fast pump-probe measurements on MgB2 [12, 13] did not find any evidence for a double relaxation down to the ps regime. 

Fig. 15 Rate data for photoinduced charge separation and subsequent charge recombination in the dyads 18(h)- Charge separation rates, cs, in THF at 20°C were determined both from fluorescence lifetimes92,102 and by pump-probe (time-resolved transient absorption) spectroscopic measurements.105 The mean lifetimes towards charge recombination, rcn were obtained from time-resolved conductivity measurements in 1,4-dioxane.99 101,103,104...

Reasonable exponential fits were obtained for the distance dependence of the photoinduced charge separation rates (in THF) for 18(w), obtained from both fluorescence92 and pump-probe measurements,105 and they are shown in Fig. 17. The phenomenological damping factors derived from the two sets of measurements are ... 

Temperature-independent anharmonic decay rates of high-frequency modes of myoglobin have been observed in time-resolved spectroscopic studies. Pump-probe vibrational spectra of the amide I band, between 1600 and 1700 cm 1, measured at temperatures from 6 K to 310 K reveal decay rates ranging only from 0.5 to 1 ps-1 [25], similar to the values we calculate. Similarly, pump-probe studies on myoglobin-CO reveal that the decay of the CO stretch, about 1950 cm is also essentially independent of temperature over the same temperature range [28]. 

This technique utilizes a pulse pump-probe experiment and monitors the absorption of a weak probe beam in the presence of a strong pump beam. Fig. 8 depicts the experimental set-up for a two-beam pump-probe experiment, which includes homodyne and heterodyne Kerr gate measurements and polarization-controlled transient absorption measurement. Generally, the input beam is produced from an amplified pulse laser system with 1 KHz repetition rate, which can produce picosecond or femtosecond pulses. This pumping light beam is divided into two beams by a beam-splitter with an intensity ratio of 30 1 therefore, the one with the stronger intensity will act as the pump and the weaker one will be the probe. The position of the sample is where these two beams focus and overlap spatially. The time delay between the pulses from these two beams is controlled by a retroreflec-... 

An electronic or vibrational excited state has a finite global lifetime and its de-excitation, when it is not metastable, is very fast compared to the standard measurement time conditions. Dedicated lifetime measurements are a part of spectroscopy known as time domain spectroscopy. One of the methods is based on the existence of pulsed lasers that can deliver radiation beams of very short duration and adjustable repetition rates. The frequency of the radiation pulse of these lasers, tuned to the frequency of a discrete transition, as in a free-electron laser (FEL), can be used to determine the lifetime of the excited state of the transition in a pump-probe experiment. In this method, a pump energy pulse produces a transient transmission dip of the sample at the transition frequency due to saturation. The evolution of this dip with time is probed by a low-intensity pulse at the same frequency, as a function of the delay between the pump and probe pulses.1 When the decay is exponential, the slope of the decay of the transmission dip as a function of the delay, plotted in a log-linear scale, provides a value of the lifetime of the excited state. 

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