[gmx-users] angle between benzene rings

[Sanku M]

Dear gromacs users
 I would like to compute the angle of orientation between two benzene rings that I have simulated using gromacs. 
I think, for this, I have to get the vector normal to the plane of the benzene ring and then get the angle of among the unit vectors. Is there any tools in gromacs that can help me to do this? Does g_sgangle work here?
Sanku