Triplet state energy of the humic substances determined by photoacoustic calorimetry

MARTIN, MARCELA V.; MIGNONE, RICARDO A.; GONZALEZ, MÓNICA; MÁRTIRE, DANIEL O.; BORSARELLI, CLAUDIO

La Serena

Encuentro; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (XELAFOT); 2010

In this communication we performed Laser-Induced Optoacoustic Spectroscopy (LIOAS) experiments with Aldrich Humic Acid (AHA), Pony Lake (PLFA) and Waskish Peat (WPFA) Fulvic Acids (FA) to obtain information on the properties of long-lived species formed after irradiation with light of humic substances (HS). The species which stores the energy in the LIOAS experiments could be triplet states or radical cations of the HS formed from the triplet states. The calculated energy content for the lowest excited triplet state of the buffle model is 38 kcal mol-1. This value is very close to that reported (Bruccoleri, A. et all, 1990) for fulvic acids (41-43 kcalmol-1) and can be taken as an upper limit of Est. Taking Est = 38 kcal mol-1 and the values of Estst obtained from the optoacoustic experiments, st was calculated. The values of st are on the order of those reported for the primary quantum yields of formation of the solvated electrons, which supports the assignment of the energy-storing species to the radical cation.