Using the Short-Wavelength-Spectrometer on the Infrared Space Observatory ( ISO ) , we obtained near- and mid-infrared spectra toward the brightest H _ { 2 } emission peak of the Orion OMC-1 outflow .
A wealth of emission and absorption features were detected , dominated by 56 H _ { 2 } ro-vibrational and pure rotational lines reaching from H _ { 2 } 0–0 S ( 1 ) to 0-0 S ( 25 ) .
The spectra also show a number of H i recombination lines , atomic and ionic fine structure lines , and molecular lines of CO and H _ { 2 } O .
Between 6 and 12 \mu m the emission is dominated by PAH features .

The extinction toward the molecular and atomic line emitting regions is estimated from relative line intensities , and it is found that the H _ { 2 } emission arises from within the OMC-1 cloud at an average K-band extinction of 1.0 mag , whereas the atomic hydrogen emission and much of the fine structure emission comes from the foreground H ii region and its bounding photodissociation front .

The total H _ { 2 } luminosity in the ISO-SWS aperture is estimated at ( 17 \pm 5 ) ~ { } L _ { \sun } , and extrapolated to the entire outflow , ( 120 \pm 60 ) ~ { } L _ { \sun } .
The H _ { 2 } level column density distribution shows no signs of fluorescent excitation or a deviation from an ortho-to-para ratio of three .
It shows an excitation temperature which increases from about 600 K for the lowest rotational and vibrational levels to about 3200 K at level energies E ( v,J ) / k > 14 000 K. No single steady state shock model can reproduce the observed H _ { 2 } excitation .
The higher energy H _ { 2 } levels may be excited either thermally in non-dissociative J-shocks , through non-thermal collisions between fast ions and molecules with H _ { 2 } in C-shocks , or they are pumped by newly formed H _ { 2 } molecules .
The highest rotational levels may be populated by yet another mechanism , such as the gas phase formation of H _ { 2 } through H ^ { - } .