Pulsed photo acoustic evaluation of intersystem crossing quantum yields in fulvic acid

Evaluation of primary photoproduct quantum yields in fulvic acid

“…£T -£TS/ ri-j-g (5) where nTS = • and Ep is the energy of a 337.1-nm photon which is equal to 5.9 X 10-19 J; therefore, the energy (in J mol-1) of the triplet state is equal to (5.9 X 10"19 J) -(5.9 X 1CT19 J)(ED8)/E¡ A £T =---^-- (6) This equation gives a direct relation between the photoacoustic signal, the absorbance, the energy, and the quantum yield of the triplet state in the fulvic acid mixture (4,5).…”

“…Instrumentation. The apparatus for the photoacoustic measuredments is described in detail elsewhere (4,5). It is driven by a PRA LN100 nitrogen laser (Photochemical Research Associates) which produces 10-60 µj pulses at 337.1 nm with a pulse width of approximately 300 ps.…”

“…This technique has emerged as a powerful tool for estimates of energetics of photophysical processes. A preliminary account of its application to fulvic acid has been given in ref 4. The signal obtained is the intensity of the acoustic pulse reaching the wall of the piezoelectric tube as a function of time.…”

“…As opposed to present measurements, where the constant is the instrument sensitivity cited above, steadystate photoacoustic spectra measure all energy dissipated in thermal form and, hence, give a signal proportional to the difference of energy absorbed minus energy emitted as luminescence. For Armadale fulvic acid, luminescence yields are difficult to estimate precisely but are certainly less than about 0.03 at pH 7.0 (3,4), so a steady-state signal for the fulvic acid is proportional to absorbance within experimental error. In contrast, the present pulsed experiment measures energy converted into thermal energy within the apparatus time constant of about 2 µ$.…”

Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties

“…Bruccoleri et al applied magnetic circular dichroism (MCD) spectroscopy to an organic matter isolate and assigned an absorbance transition as S 0 / T 1 , and the wavelength for this transition (714 nm; 14 000 cm À1 ) corresponded to an energy of 170 kJ mol À1 . 57,58 Mazhul et al used room temperature phosphorescence spectroscopy to identify the opposite transition (T 1 / S 0 ), with an onset near 405 nm, corresponding to the highest energy (phosphorescing) triplets having an E T value of 300 kJ mol À1 . 59 In both of these studies, the estimates of E T must be viewed with caution, as both techniques are almost certainly confounded by the complex mixture of DOM.…”