Humic materials absorption spectra

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Laser flash photolysis studies of the well characterised soil humic substance, Armadale Fulvic Acid (P.E.I., Canada), have been carried out, with excitation at 355 nm on picosecond and nanosecond time scales. Three principal transient absorption sijtnals have been observed in aqueous solution a component with a maximum absorption at 675 nm and a lifetime of about J microsecond (at pH = 7.0), a second component with a maximum absorption at <175 nm and a lifetime of I -10 microseconds, and a third component with a broad, featureless transient absorption spectrum and a lifetime in excess of LUO microseconds. The 675 nm signal is believed to be a solvated electron on the basis of lifetime and quenchinjt data, and is observed 20 ps after excitation. The 475 nm signal is believed to he a radical cation on the basis of its concurrent appearance with the electron at 20 ps. The third featureless component emerges nanoseconds after excitation and is believed to correspond to the triplet states of the humic material. 

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