  Merging systems at low redshift provide the unique opportunity to study the
processes related to star formation in a variety of environments that
presumably resemble those seen at higher redshifts. Previous studies of distant
starbursting galaxies suggest that stars are born in turbulent gas, with a
higher efficiency than in MW-like spirals. We have investigated in detail the
turbulent-driven regime of star-formation in nearby colliding galaxies
combining high resolution VLA B array HI maps and UV GALEX observations. With
these data, we could check predictions of our state-of-the-art simulations of
mergers, such as the global sharp increase of the fraction of dense gas, as
traced by the SFR, with respect to the diffuse gas traced by HI during the
merging stage, following the increased velocity dispersion of the gas. We
present here initial results obtained studying the SFR-HI relation at 4.5 kpc
resolution. We determined SFR/HI mass ratios that are higher in the external
regions of mergers than in the outskirts of isolated spirals, though both
environments are HI dominated. SFR/HI increases towards the central regions
following the decrease of the atomic gas fraction and possibly the increased
star-formation efficiency. These results need to be checked with a larger
sample of systems and on smaller spatial scales. This is the goal of the
on-going Chaotic THINGS project that ultimately will allow us to determine why
starbursting galaxies deviate from the Kennicutt-Schmidt relation between SFR
density and gas surface density.
