Triplet states of humic acids studied by laser flash photolysis using different excitation wavelengths

摘要

The spectra and kinetics of short-lived intermediates formed from aqueous (0.1 N NaOH)solutions of the natural mixture of humic and fulvic acids (HFA)were studied by laser flash photolysis using excitation wavelengths of 337,390,470,and 520 nm.Laser photolysis of HFA with light of 520 and 470 nm results in the formation of triplet excited states (T_(HFA))characterized by the broad absorption spectrum with a maximum near 630 nm and lifetimes of approx0.15 ms in deoxygenated solutions.The formation of two types of T_(HFA)with lifetimes of approx0.1 and 2 ms and absorption spectra with maxima at 570 nm is observed under photolysis with light of 337 and 390 nm.The estimation of quantum yields of T_(HFA)gives approxl and 0.3% under photolysis with excitation wavelengths of 337 and 520 nm,respectively.The rate constants of T_(HFA)quenching by molecular oxygen are equal to (7-8)(centre dot)10~8 Lmol~(-1)s~(-1).