Femtosecond techniques

Nanosecond techniques have now been superceded by picosecond and femtosecond techniques, allowing detection in time domains as short as 10 s. Yet, nanosecond techniques remain powerful tools in the arsenal of the physical organic chemist quite simply, many radical, carbene, carbocation, carbanion reactions take place in the nano- and microsecond time scales. 

Expansion of the time scale to monitor phenomena in other time scales. Picosecond and femtosecond techniques are well established. Use of nLFP for very long time scales (10 ms to s) requires very stable light sources, and frequently, long optical path cells. 

Recently, there has been much interest in the development and application of multidimensional coherent nonlinear femtosecond techniques for the study of electronic and vibrational dynamics of molecules [1], In such experiments more than two laser pulses have been used [2-4] and the combination of laser pulses in the sample creates a nonlinear polarization, which in turn radiates an electric field. The multiple laser pulses create wave packets of molecular states and establish a definite phase relationship (or coherence) between the different states. The laser pulses can create, manipulate and probe this coherence, which is strongly dependent on the molecular structure, coupling mechanisms and the molecular environment, making the technique a potentially powerful method for studies of large molecules. 

Very short time-resolution techniques are being increasingly applied to the study of very fast processes, for example solvent relaxation and electron-transfer to and from electronically excited species (Peters inter alia). Real time femtosecond techniques now provide a probe for the study of transition states (Dantos et al.). This is a very promising development. The First International Laser Conference was held in 1987 - in part a... 

We predict an increased role in picosecond/femtosecond techniques, and have begun such measurements in our laboratory for the CO2-HX and N2O-HX systems discussed in Section III. 

As usual, we start with our personal and highly subjective assessments of important developments in the more physical areas of photochemistry. It is now evident that lasers have largely taken over from lamps as radiation sources in this area of the subject. This year, we note a somewhat increased interest in practise and decreased activity on the theoretical side. Femtosecond techniques are now well established. 

At the critical distance of 6.9 A, the energies of the excited and ground states are very close and there is a 20% chance that the excited state will dissociate to give separate Na and I atoms. The femtosecond technique detects a decaying signal from the excited state and an increasing signal as bursts of Na atoms appear from each vibration (Fig. 11). 

Some systems studied by sub>picosecond and femtosecond techniques... 

BRATOS - Apart from the electron solvation processes are there other reactive or prereactive processes where the use of femtosecond techniques is necessary ... 

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