Ultraviolet/visible spectroscopy accuracy

The basic methods of the identification and study of matrix-isolated intermediates are infrared (IR), ultraviolet-visible (UV-vis), Raman and electron spin resonance (esr) spectroscopy. The most widely used is IR spectroscopy, which has some significant advantages. One of them is its high information content, and the other lies in the absence of overlapping bands in matrix IR spectra because the peaks are very narrow (about 1 cm ), due to the low temperature and the absence of rotation and interaction between molecules in the matrix. This fact allows the identification of practically all the compounds present, even in multicomponent reaetion mixtures, and the determination of vibrational frequencies of molecules with high accuracy (up to 0.01 cm when Fourier transform infrared spectrometers are used). 

In ultraviolet, visible, and infrared spectroscopy, one usually measures the spectral line wavelengths (rather than frequencies), using a prism or diffraction grating. Until 1972, the speed of light was not known to very high accuracy, so it became traditional to convert measured wavelengths to reciprocal wavelengths 1 /A (rather than to frequencies) the quantity 1 /A is called the wave number. 

Absorption spectroscopy based on ultraviolet and visible radiation is one of the must useful tools available to the scientist for quantitative analysis. Important characteristics of spectrophotomctric and photometric methtxls include (1) wide applicability to both organic and inorganic systems. (2) typical detection limits of 10 to 10 M (in some cases, certain modifications can lead to lower limits of detection), (. ) moderate to high selectivity. (4) good accuracy (typically, relative uncertainties arc I % to. V /o. although with special precautions, errors can be reduced to a few tenths of a percent), and (5) case and convenience of data acquisition. 

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