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We present high spatial resolution (0.6 arcsec) near-infrared broad-band JHKimages and Br_gamma 2.1661 micron and H_2 1-0 S(1) 2.122 micron emission lineimages of the nuclear regions in the interacting starburst galaxies NGC 520,NGC 1614 and NGC 7714. The near-infrared emission line and radio morphologiesare in general agreement, although there are differences in details. In NGC1614, we detect a nuclear double structure in Br_gamma, in agreement with theradio double structure. We derive average extinctions of A(K) = 0.41 and A(K) =0.18 toward the nuclear regions of NGC 1614 and NGC 7714, respectively. For NGC520, the extinction is much higher, A(K) = 1.2 - 1.6. The observed H_2/Br_gammaratios indicate that the main excitation mechanism of the molecular gas isfluorescence by intense UV radiation from clusters of hot young stars, whileshock excitation can be ruled out.  The starburst regions in all galaxies exhibit small Br_gamma equivalentwidths. Assuming a constant star formation model, even with a lowered uppermass cutoff of M_u = 30 M_o, results in rather old ages (10 - 40 Myr), indisagreement with the clumpy near-infrared morphologies. We prefer a model ofan instantaneous burst of star formation with M_u = 100 M_o, occurring 6 - 7Myr ago, in agreement with previous determinations and with the detection ofW-R features in NGC 1614 and NGC 7714. Finally, we note a possible systematicdifference in the amount of hot molecular gas between starburst and Seyfertgalaxies.Comment: 13 pages, A&A, accepte

Near-infrared line imaging of the starburst galaxies NGC 520, NGC 1614 and NGC 7714