Images of the nuclear region of NGC 6240 taken in the 2.122 micron, ν= 1-0 S(1) quadrupole line of molecular hydrogen demonstrate that the line emission is extended and distinct from the two nuclei producing most of the continuum emission. A region ~ 2" southwest of the southern nucleus produces almost 20% of the total line radiation, yet has no detectable 2 micron continuum. The H_2_ lines are asymmetric, with very little emission on the short-wavelength side of the line peaks. These results indicate that a global phenomenon, such as the dissipative collision of two disks of molecular material, is taking place. The presence of shock-excited material at the same velocity throughout the central kpc of the galaxy and the asymmetry in the S(1) line profile support this conclusion. Global shocks may power the far-infrared luminosity of NGC 6240 as well; if so, the strong H_2_ and infrared emission can persist for no more than ~ 10^6^ yr.
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Herbst et al. (1990) studied this question.