Neutron diffraction measurements were carried out on H/ D isotopically substituted water in the low-density supercritical condition (T = 673 K, P = 26.3 MPa, and ρ = 0.0068 molecules-Å-3) in order to obtain direct information on the intermolecular partial structure functions, gHH inter(r), gOHinter(r), and gOOinter(r). In correspondence to the high-density supercritical water previously reported, the intermolecular nearest neighbor peaks in gHHinter(r), gOH inter(r), and gOOinter(r) are diffuse compared with the ambient ones. The nearest neighbor O⋯O distance (3.3 Å) and its coordination number (2.6) were determined from the observed gOO inter(r). These results indicate that the orientational correlation between neighboring water molecules is considerably lost in low-density supercritical water. Small clusters involving a few water molecules are preferentially formed in low-density supercritical water, which is consistent with results obtained by previous IR and NMR studies.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry