Hydration structure of CO2-absorbed 2-aminoethanol studied by neutron diffraction with the 14N/15N isotopic substitution method.

Neutron diffraction measurements were carried out for CO2-absorbed aqueous 11 mol % 2-aminoethanol (MEA) D2O solutions (corresponding to 30 wt % MEA solution) in order to obtain information on both the intramolecular structure and intermolecular hydration structure of the MEA carbamate molecule in the aqueous solution. Neutron scattering cross sections observed for (MEA)0.11(D2O)0.89, (MEA)0.11(D2O)0.89(CO2)0.06, and (MEA)0.11(D2O)0.89(DCl)0.11 solutions with different 14N/15N ratios were used to derive the first-order difference function, ΔN(Q), which involves environmental structural information around the nitrogen atom of the MEA molecule. Intramolecular geometry and intermolecular hydration structure of MEA, protonated MEA (MEAD+), and MEA carbamate (MEA-CO2) molecules were obtained through the least-squares fitting of the observed ΔN(Q) in the high-Q region and the intermolecular difference function, ΔNinter(Q), respectively. In the aqueous solution, the MEA molecule takes the gauche conformation (di...