  In {\gamma} Doradus stars, gravito-inertial modes in the radiative zone and
inertial modes in the convective core can interact resonantly, which translates
into the appearance of dip structures in the period spacing of modes. Those
dips are information-rich, as they are related to the star core
characteristics. Our aim is to characterise these dips according to stellar
properties and thus to develop new seismic diagnostic tools to constrain the
internal structure of {\gamma} Doradus stars, especially their cores. We used
the two-dimensional oscillation code TOP to compute sectoral prograde and
axisymmetric dipolar modes in {\gamma} Doradus stars at different rotation
rates and evolutionary stages. We then characterised the dips we obtained by
their width and location on the period spacing diagram. We found that the width
and the location of the dips depend quasi-linearly on the ratio of the rotation
rate and the Brunt-V\"ais\"al\"a frequency at the core interface. This allowed
us to determine empirical relations between the width and location of dips as
well as the resonant inertial mode frequency in the core and the
Brunt-V\"ais\"al\"a frequency at the interface between the convective core and
the radiative zone. We propose an approximate theoretical model to support and
discuss these empirical relations. The empirical relations we established could
be applied to dips observed in data, which would allow for the estimation of
frequencies of resonant inertial modes in the core and of the
Brunt-V\"ais\"al\"a jump at the interface between the core and the radiative
zone. As those two parameters are both related to the evolutionary stage of the
star, their determination could lead to more accurate estimations of stellar
ages.
