Measurements of hyperne splittings in the ground electronic state of I2 have been performed by stimulated Raman spectroscopy. An argon laser emitting at 514.5 nm, drives the coherence between hyperne levels of the J 00 =1 3 orJ 00 = 15 rotational levels of the ground vibronic state, via resonant excitation of the hyperne transitions of the optical resonances (43-0) P(13) or R(15). We study the influence of the various experimental parameters on the line shape: the beam geometry, the laser modulation spectrum, the laser power, the molecular frequency shifts. We show that only beam aberrations can give rise to a signicant asymmetry of the line shape, which contributes to an error in the determination of the resonance frequency. From a theoretical expression of the line shape taking into account the beam geometry, a detailed study of this error is performed. The theoretical predictions and the experimental results are in very good agreement. From the measurements, improved sets of hyperne interaction constants for the I2 molecule have been calculated for J 00 =1 3 andJ 00 = 15. These constants are identical for both levels, except for quadrupole coupling constant eqQ which exhibits a J-dependence, which we attribute to the centrifugal distortion of the molecule. PACS. 33.15.Pw Fine and hyperne structure { 33.70.Jg Line and band widths, shapes, and shifts