It is known that the rotational equation of motion of rigid molecules in MD simulations can be solved in a singularity-free form if quaternions are used for the description of the rotational motion. We show that these quaternions are also suited for the calculation of the so-called ‘g-coefficients’, which are the expansion coefficients of the molecular pair correlation function (MPCF) in terms of Wigner functions. This is due to the fact that quaternions arc themselves a representation of the rotation group and can be referred to an arbitrary coordinate frame in a particularly simple way. As an application for the quaternion formalism we calculate some g-coefficients of the MPCF of methylene chloride (CH2 Cl2 ).