Electronic rearrangement upon the hydrolyzation of aqueous formaldehyde studied by core-electron spectroscopies

We have combined near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) to study the electronic rearrangement associated with the hydrolyzation of formaldehyde to methanediol in aqueous solution. The spectra are contrasted against those of aqueous formamide and urea, which are structurally similar but do not undergo hydrolysis in solution. We have recently demonstrated that the hydrolyzation of formaldehyde is manifested in the oxygen 1s NEXAFS spectrum by the disappearance of the oxygen 1s --> pi* absorption line. This is a characteristic signature that the C=O double bond has been broken. In the present study we extend our investigation to include carbon 1s NEXAFS and XPS spectra of the three solutions. The carbon NEXAFS spectra show the C 1s --> pi* absorption line for each solute except for formaldehyde. Moreover, the carbon 1s photoelectron spectra exhibit a single peak for each solute. These observations point to a near complete hydrolyzation of formaldehyde, whereas formamide and urea remain intact in the solution. The analysis is further supported by density functional theory (DFT) calculations, showing a C 1s chemical shift of approximately 1.0 eV between hydrolyzed and nonhydrolyzed forms, which would give distinguishable features in the photoemission spectrum, if coexisting forms were present in the solutions.