  We have observed three luminous infrared galaxy systems (LIRGS) which are
pairs of interacting galaxies, with the Galaxy H$\alpha$ Fabry-Perot system
(GH$\alpha$FaS) mounted on the 4.2m William Herschel Telescope at the Roque de
los Muchachos Observatory, and combined the observations with the Atacama Large
Millimeter Array (ALMA) observations of these systems in CO emission to compare
the physical properties of the star formation regions and the molecular gas
clouds, and specifically the internal kinematics of the star forming regions.
We identified 88 star forming regions in the H$\alpha$ emission data-cubes, and
27 molecular cloud complexes in the CO emission data-cubes. The surface
densities of the star formation rate and the molecular gas are significantly
higher in these systems than in non-interacting galaxies and the Galaxy, and
are closer to the surface densities of the star formation rate and the
molecular gas of extreme star forming galaxies at higher redshifts. The large
values of the velocity dispersion also show the enhanced gas surface density.
The HII regions are situated on the ${\rm{SFR}}-\sigma_v$ envelope, and so are
also in virial equilibrium. Since the virial parameter decreases with the
surface densities of both the star formation rate and the molecular gas, we
claim that the clouds presented here are gravitationally dominated rather than
being in equilibrium with the external pressure.
