Orientational correlations in low density water steam

Following an experiment performed on SANDALS in 1994 on deuterated water steam at 580K [11], we propose to measure the diffraction cross-section of three isotopically substituted samples of water at the same temperature and the lowest density probed at that time, i.e. at P = 60.3 bar, corresponding to a vapor density of: 2.79 10^(-3) atoms/Å^3. We require for this experiment 4 days of beam time on NIMROD. The present detector configuration of NIMROD guarantees acquisition of enough statistics on all three samples. Moreover the availability of the EPSR code, not yet available at the time of the first experiment, will allow to extract the three site-site radial distribution function and get better insight into the orientational correlations between water molecule at this low density state.