In addition to the tensor values in the principal axes system (PAS) it is necessary to define the orientation of the PAS tensor. Her e you have the choice to do this directly with respect to the cone axes system (CF) or indirectly by using a molecule fixed axes system (MF) as an intermediate coordinate system. The latter can be advantageous in some cases, especially when the PAS-tensor is not axial symmetric.

When using cone frame, Weblab assumes, that the z principal axis of the PAS tensor is lying on the cone. (See also topic ⇒ Cone Model) The euler angles for each site i are then given by the set (α, θ, 180o-φi). In addition to cone and jump angle you only have to define euler angle α, which defines the relative orientation of the prinicpal x-axis. This is meaningless, however, if the tensor is axial symmetric.

If you choose molecular frame, you have to enter the euler angles for the transformation from the PAS system to the molecular frame (MF) and from the molecular frame to the cone frame (CF). In this case, the z-axis of the MF is considered to lie on the cone.

In both cases, the final spectrum is obtained by integrating over all orientations given by αL and βL.

tensor relative to cone frame
tensor relative to molecular frame

Weblab uses euler angles according to the convention of Rose. For a description see here.