INVESTIGATION OF THE ORIENTATIONAL CORRELATION OF THE MOLECULES IN LIQUID H2S WITH REVERSE MONTE-CARLO SIMULATION

Reverse Monte Carlo simulation of liquid H2S has been performed on the basis of an X-ray and a neutron diffraction experiment, and the resul ting structure is analysed in detail. Partial pair correlation functio ns, spatial distribution of the molecules around each other and the pr eferred relative orientation of the nearest neighbours are investigate d. The orientational correlation of the molecules is discussed in term s of the coefficients of the spherical harmonic expansion of the orien tational pair correlation function. It is found that H2S is not a clos ely packed liquid: the average first-shell coordination number of the molecules is about 8. This is found to be a direct consequence of the molecular shape, i.e., the excluded volume of the H atoms prevents the central molecule from bring surrounded by more first-shell neighbours . The relative orientation of the molecules is found to be almost comp letely uncorrelated. Moreover, even the existing small correlation is confined to a rather small distance range and vanishes beyond about th e third nearest neighbour.