this is a summation over the scattering contributions of all atoms independent of the molecular structure. is the main contribution and easily obtained if the atomic composition of the gas (sum formula) is known. The most interesting contribution is the molecular scattering, because it contains information about the distance between all pairs of atoms in a molecule (bonded or non-bonded): with being the parameter of main interest: the atomic distance between two atoms, being the mean square amplitude of vibration between the two atoms, the anharmonicity constant (correcting the vibration description for deviations from a purely harmonic model), and is a phase factor, which becomes important if a pair of atoms with very different nuclear charge is involved. The first part is similar to the atomic scattering, but contains two scattering factors of the involved atoms. Summation is performed over all atom pairs. is negligible in most cases and not described here in more detail. is mostly determined by fitting and subtracting smooth functions to account for the background contribution. So it is the molecular scattering intensity that is of interest, and this is obtained by calculation all other contributions and subtracting them from the experimentally measured total scattering function. Results Figure 5 shows two typical examples of results. The molecular scattering intensity curves are used to refine a structural model by means of a least squares fitting program. This yield precise structural information. The Fourier transformation of the molecular scattering intensity curves gives the radial distribution curves (RDC). These represent the probability to find a certain distance between two nuclei of a molecule. The curves below the RDC represent the diffrerence between the experiment and the model, i.e. the quality of fit. The very simple example in Figure 5 shows the results for evaporated white phosphorus, P4. It is a perfectly tetrahedral molecule and has thus only one P-P distance. This makes the molecular scattering intensity curve a very simple one; a sine curve which is damped due to molecular vibration. The radial distribution curve (RDC) shows a maximum at 2.1994 Å with a least-squares error of 0.0003 Å, represented as 2.1994(3) Å. The width of the peak represents the molecular vibration and is the result of Fourier transformation of the damping part. This peak width means that the P-P distance varies by this vibration within a certain range given as a vibrational amplitude u, in this example uT(P‒P)