The most valuable information is carried by the intensity of molecular scattering I a ( s ) , as it contains information about the distance between all pairs of atoms in the molecule. It is given by I m ( s ) = K 2 R 2 I 0 ∑ ∑ i = 1 N ∑ ∑ i ≠ ≠ j j = 1 N | f i ( s ) | | f j ( s ) | sin ⁡ ⁡ [ s ( r i j − − κ κ s 2 ) ] s r i j e − − ( 1 / 2 l i j s 2 ) cos ⁡ ⁡ [ η η i ( s ) − − η η i ( s ) ] , where r i j is the distance between two atoms, l i j is the mean square amplitude of vibration between the two atoms, similar to a Debye–Waller factor, κ κ is the anharmonicity constant and η η a phase factor which is important for atomic pairs with very different nuclear charges. The summation is performed over all atom pairs. Atomic triplet intensity I t ( s ) is negligible in most cases. If the molecular intensity is extracted from an experimental pattern by subtracting other contributions, it can be used to match and refine a structural model against the experimental data.