Pump-probe techniques transfer

Other classes of reactions that have received much attention are proton transfer and electron transfer reactions. These processes can often be initiated by light. This characteristic has made it possible to monitor their time evolution by ultrafast pump-probe techniques. An example is the acid-base reaction of 1-naphthol with ammonia. On the ground electronic surface... 

Transient pump-probe techniques are particularly well poised for the study of fast electron and energy transfer... 

Recent intensive investigations using pump-probe techniques and femtosecond anisotropy measurements have revealed that ultrafast energy transfer ( 80 fsec) from one of the two accessory bacteriochlorophyUs to the special pair and internal conversion ( 120 fsec) within the special pair occur prior to electron transfer from the special pair to one of the two bacteriopheophytins. 

In order to learn about the true quantum efficiency of photogeneration one therefore has to study the photoinduced charge generation mechanism at faster time scales. Pump probe spectroscopy utilising a few optical-cycle laser pulses (5-6 fs) in the visible spectral range with broadband frequency conversion techniques [89] now makes it possible to study extremely fast optically-initiated events with unprecedented time resolution. Such a setup was used to time-resolve the kinetics of the charge transfer process from a polymer chain to a fullerene moiety in thin films of poly[2-methoxy, 5-(3, 7 -dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) and [6,6]-phenyl C6i butyric acid methyl ester (PCBM). Solutions prepared from 1 wt% solutions of toluene on thin quartz substrates were studied. 

The initial charge separation in PS I and PS II can be followed by what are known as ultrafast optical spectroscopy techniques. Several variations on this method exist, but they can be grouped into pump-probe absorbance difference and transient fluorescence methods (25, 26). In the first instance, the sample is irradiated with a pump pulse to initiate the electron transfer and the absorbance is measured using a probe pulse at a... 

In CV, substrates are generally activated during the first scan by electron transfer and the reverse scan is then used to detect the activated substrates. The formation of other electrochemically active intermediates or products can also be revealed by these scans or possibly by the performance of multiscans. The CV technique is, like DPSC, similar to the pump/probe experiment known from photochemistry, but in CV, unique knowledge about the thermodynamic properties of the intermediates... 

Wang et al, 2003 Wang et al, 2004). The time resolution of this technique is inversely proportional to the spectral resolution. With 10 cm spectral resolution, a time resolution of -1.5 ps can be obtained. These probe techniques can be combined with an excitation pulse in a pump/probe scheme to measure interface selective dynamics. They have been used to study solvation dynamics at a liquid-liquid interface (Zimdars et al, 1999) and vibrational relaxation on a metal surface (Bonn et al, 2000 Bonn et al, 2001). Although not yet reported, the technique should also be applicable to the study of interfacial electron-transfer dynamics. 

One example of this pump-and-probe technique is the investigation of collision-induced vibrational-rotational transitions in the different isotopes HDCO and D2CO of formaldehyde by an infrared-UV double resonance [1041]. A CO2 laser pumpes the V6 vibration of the molecule (Fig. 8.18). The collisional transfer into other vibrational modes is monitored by the fluorescence intensity induced by a tunable UV dye laser with variable time delay. 

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