Intermediate range O-O correlations in supercooled water down to 235 K.

Wide angle x-ray scattering of supercooled water down to 234.8 K was studied using high energy x rays at the European Synchrotron Radiation Facility. The oxygen-oxygen pair distribution function (PDF) was calculated from the scattering pattern out to the 5th peak at an intermolecular distance, r ≈ 11 Å. We observe that the 4th peak and the 5th peak in the PDF increase in height upon supercooling. We also observe that the 4th peak position (r4) shifts to shorter distances upon supercooling consistent with previous studies, but we see a more rapid change at the lowest temperature. The running oxygen-oxygen coordination number is calculated for 5 different temperatures, and an isosbestic point at riso = 3.31 ± 0.05 Å was found corresponding to a coordination number of 4.39 ± 0.15. The comparison of the PDF of the coldest water with that of amorphous ice shows distinct differences. We propose that there are 5-member pentamer rings in low density liquid-like structures giving rise to the sharp correlations at r ≈ 9 Å and r ≈ 11 Å.