Effects of gas-liquid interface on the theoretical X-ray absorption spectroscopy of phenylenediamines

In this study, we performed molecular dynamics simulations for m-, o-, and p-phenylenediamine both in the bulk aqueous solution and at the gas-liquid interface. Polar-angle distributions were obtained to characterize the molecular orientation. Theoretical X-ray absorption spectra were calculated to evaluate the effects of the aqueous solution and gas-liquid interface on the electronic structures of phenylenediamines using density functional theory. The bulk aqueous solution and gas-liquid interface environments allow transitions that are forbidden for isolated p-and m-phenylenediamine. The spectra sampled at different polar angles show diverse lineshapes, which are sensitive to the microenvironment. The histogram-based gradient boosting regression tree was used to obtain the center line of spectra group consisting of 100 sampled spectra for each isomer in the bulk aqueous solution or at the gas-liquid interface. Several machine learning classifiers were further applied to classify the bulk aqueous solutions and gas-liquid interfaces. This study provides insight into the molecular dynamics at the gas-liquid interface and the aqueous solution effects on the molecular electronic structures. These theoretical X-ray absorption spectra are necessary for the assignment of experimental X-ray absorption spectroscopy.