Knowledge Bank

For over forty years kinetic spectroscopy has been a powerful means for obtaining the spectra of free radicals and for following their kinetics. Over the last decade kinetic spectroscopy has been developed in the infrared using excimer laser flash photolysis to produce the radicals and single frequency cw infrared lasers to probe their transient infrared absorption spectra. Using this approach, a number of spectroscopic and kinetic investigations have been carried out in several laboratories. To illustrate the range and versatility of the method, some of these investigations will be described. The most critical component of the experiment is the infrared probe laser which must be highly monochromatic and which ideally should be broadly tunable. No single laser source having these requisites that covers the entire infrared fingerprint region exists. Thus depending on the wavelength region of interest, color center lasers, difference frequency generation in $LiNbO3$, and a variety of ternary salt infrared diodes have been used. Recently we have been developing a very broadly tunable source based on difference frequency generation in $AgGaS2$ by mixing cw dye and Ti:sapphire lasers. This source, which has the desired qualities of high monochromaticity and conveniently long scans (up to 5 to $10cm-1$), is capable of operating throughout the region 1050 to $3100cm-1$ using only three gain media (Rh6G, DCM, and Ti:sapphire) in the two lasers. This laser will permit a wide variety of infrared kinetic spectroscopy investigations to be carried out conveniently and straightforwardly.