Given by \[\Delta \theta _{i- jkl}=\frac{\Delta z_{j}}{r_{eij}}\ \sin \mathit{\Phi }_{kil}\] where the numbering of the atoms is given in the diagram. \(\mathit{\Phi} _{kil}\) denotes the @A00346@ between the bonds \(ik\) and \(il\), \(\Delta z_{j}\) the perpendicular distance of the atom \(j\) from the instantaneous plane \(ikl\) and \(r_{eij}\) the equilibrium length of the bond \(ij\).