Multichannel spectrometers acquisition techniques

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

With slow kinetics of the involved processes or with interfaces where electrode potential modulation might be detrimental because of crystallographic changes in the metal surface, other spectroscopic techniques have to be used. The whole spectrum of interest can be scanned or registered within a few milliseconds with a rapid scan spectrometer or a multichannel (diode array) spectrometer. Repeated acquisition provides the required signal-to-noise ratio. After a potential step, the acquisition is repeated and spectral calculation yields AR/R. This single potential step procedure allows investigation of systems where repeated potential modulation has failed. 

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