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In this paper we present a thorough study of the local microscopic structure of carbon dioxide in a wide thermodynamic region, covering both undercritical and supercritical states. From neutron diffraction measurements we derive accurate information on the neutron weighted distribution function,gnw (τ), which allows us to single out a realistic interaction potential to be used in Molecular Dynamics (MD) simulations. These MD simulations are then performed to supplement the information obtained from the neutron scattering experiments. In such a way we determine appropriateaverages of the molecular distribution function,g(R, ω1,ω2). The presence of preferred relative orientations between neighbouring molecules is evident. We find that, among first neighbouring molecules,T-shaped configurations are largely preferred in all the investigated thermodynamic states and that electrostatic interactions play a crucial role in determining the local structure of the fluid.

The study of spatial features in diatomic liquids and gases is reviewed with a specific emphasis on experimental measurements using neutron and X-ray diffraction. The formalism for defining the pair-correlation function is described and related to the liquid structure factor which can be extracted from the diffraction measurements. Different molecular systems can be classified in terms of the intermolecular potential which depends on various factors related to geometrical conformation, electron density distribution and anisotropy. The increased complexity over monoatomic systems gives rise to new phenomena associated with the orientational correlation of molecular axes. The techniques of neutron and X-ray diffraction are critically reviewed and a full list of published work (plus some unpublished results) is presented. The experimental measurements are analysed and compared with the results of computer simulations using model potentials. It is noted that several systems (e.g. N2, O2, F2, CO) have a relatively simple behaviour but others (e.g. Cl2, Br2, I2) are only just on the point of being properly understood, while the hydrogen-bonded liquids (e.g. HF, HCl) still pose many problems that currently remain unresolved. The review ends with a brief consideration of likely developments in the foreseeable future.

Magnetization‐vs‐temperature curves were determined in MnNi3 for different states of order in the temperature range −196° to 375°C and for fields up to 4000 Oe. Neutron‐diffraction analysis has been performed on the same specimens in order to determine both the average‐order parameter S and the size of ordered regions. The results are compared with the ones available in the literature and discussed in terms of details of the state of order.

Measurements of the mobility of positive and negative charges in the $^{3}\mathrm{He}$ critical region are reported. The experimental data show that for the two probes there is a definite lowering of the mobility at the critical point. However, within the limits of our approach to the critical point ($\frac{\ensuremath{\Delta}T}{{T}_{c}}\ensuremath{\simeq}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$; $\frac{\ensuremath{\Delta}p}{{p}_{c}}\ensuremath{\simeq}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$), no evidence of dramatic decrease in the mobility is observed. The decrease in the mobility is $\ensuremath{\approx}30%$ for either probes; however, the influence of the critical phenomena on the shape of the mobility curve differs for the two probes probably because the positive and negative carriers differ in their effective radius. Some indication of the correct value of the $^{3}\mathrm{He}$ critical temperature is also reported.

The self‐diffusion coefficient of liquid argon has been measured by the capillary technique at 84.56±0.04 °K and at about 70 cm Hg. The average value of D(A37—A40) is (1.53±0.03) 10−5 cm2/sec.

Polarized neutrons were used to determine the magnetic moments of the MnNi3 alloy. The ratio of the magnetic to the nuclear scattering amplitude was determined from the polarization ratio for a given reflection. The magnetic moments of Mn and Ni were calculated by using the magnetic form factors of metallic Ni and the Mn2+ ion. The average magnetic moment per atom was found to be approx equal l mu BETA, in agreement with experimental results.