  We have calculated the physical conditions throughout the NLR of the merger
Seyfert galaxy NGC 6240 by modelling the observed optical and infrared line
ratios. We have found that the optical spectra are emitted by clouds
photoionised by the power-law radiation flux from the AGN (or AGNs), and heated
mainly by the shock accompanying the propagation of the clouds outwards. The
infrared line ratios are emitted from clouds ejected from a starburst which
photoionises the gas by the black-body radiation flux corresponding to a
stellar colour temperature of about 50,000 K. Both the flux from the AGN and
the ionization parameters are low. The most characteristic physical parameters
are the relatively high shock velocities (>400 km/s) and low preshock densities
(about 40-60 cm-3) of the gas. The C/H, N/H, O/H relative abundances are higher
than solar by a factor lower or about 1.5. We suggest that those high relative
abundances indicate trapping of H into H2 molecules rather than high
metallicities. Adopting an initial grain radius of 1 micron, the dust
temperatures calculated in the clouds reached by the power-law radiation flux
and by the black-body radiation flux are 81 K and 68 K, respectively.
