Potential energy surface Pulse-measurements

Part of the stimulus for research in this area comes from the possibility of probing the dynamics of such processes on short time scales by using picosecond lasers. The standard pulse-and-probe experiments will measure the entire time profile of the recombination and photodissociation processes. An interpretation of such results therefore requires a consideration of the dynamics on several potential energy surfaces for both the primary and secondary recombination processes. The very short time behavior is often obscured by experimental problems (laser rise times etc.), but the secondary recombination process is more easily studied. 

Since 1970, direct photolysis of molecules or ions in low-pressure, collisionless environments, has permitted molecules to be excited to well-defined energy levels, while the use of pulsed lasers or coincidence techniques has provided an accurate external time base with which to measure the dissociation rate constants over many orders of magnitude. It is often the case that more precise experimental results lead to fundamental changes in the theoretical models which describe the phenomena. This has not happened in the case of unimolecular reactions. The statistical theory has remained surprisingly robust. Most molecular systems that dissociate on a bound potential energy surface do so in a statistical fashion. What has changed in the past 25 years is our ability to apply the statistical theory. It is now possible to calculate Unimolecular rate constants with essentially no adjustable parameters and which are in quantitative agreement with experiments. 

Besides the traditional capacitance versus voltage (C/V) measurements, which are mainly used for the characterisation of MOS and EIS capacitances, the scanned light pulse technique (SLPT) was introduced by Engstrom and Aim [13], first for MOS structures. This technique utilises a fight source to illuminate a local area of the MOS structure. Thus, a local photo-effect-induced current can be measured, which only depends on the local properties and energy states of the illuminated region of the MOS structure. In 1988, Hafeman et al. combined this SLPT method with EIS structures to develop the LAPS [14,15]. This sensor is capable of measuring the surface potential of the electrolyte-transducer interface with a lateral resolution. Hence, the surface... 

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