Lambert laser spectroscopy

There are, however, some complications that have not been taken into account in this interpretation, arising from spectroscopy. One of these is that absorption by the excited I2 molecules (formed on geminate recombination) is mostly into the lower energy levels, so the molar absorptivity is not the same for all the molecules and there will be deviations from the Beer-Lambert law. Another concerns the use of a neodymium laser to provide the excitation flash (Section 4.2.3.1). The wavelength (532 nm) is such as to produce two excited states, with consequences which may complicate calculation of the quantum yield. The difficulty may be overcome by using a lower-energy pulse from a dye laser the excited... 

Because IR absorption measurements discussed in this book are all performed in optically extremely dilute samples, such as those occurring in molecular beams or tandem mass spectrometers, action spectroscopy is employed instead of direct absorption IR spectroscopy. In conventional direct absorption IR spectroscopy, the attenuation of the light beam transmitted through the sample is measured as a function of the frequency of the IR radiation. By measuring the IR laser beam intensity before and after the sample, the absorbance as a function of the frequency of the IR photons is obtained according to the Lambert-Beer law ... 

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