The optical properties of dissolved organic matter (DOM) are of great interest to scientists and engineers, as they are used as surrogates for both concentration and properties of this material, including being used to predict photochemical reactivity. In this project, the UV-Vis spectra for DOM model compounds were calculated using time-dependent density functional theory (TD-DFT). Summing these individual spectra, it was possible to recreate the observed exponential shape of the DOM absorption spectra. Additionally, by predicting the effects of sodium borohydride reduction on the model compounds, then calculating the UV-Vis absorbance spectra of the reduced compounds, it was also possible to correctly predict the effects of borohydride reduction on DOM absorbance spectra with a larger relative decrease in absorbance at longer wavelengths. The contribution of charge-transfer (CT) interactions to DOM absorption were also evaluated and the calculations showed that <i>intra</i>-molecular CT interactions could take place, while <i>inter-molecular</i> CT interactions are proposed to be less likely to contribute.

Computational calculation of dissolved organic matter absorption spectra

ACS Spring 2022

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