High resolution fourier transform spectroscopy of H2IR emission in NGC 7023

A Fourier transform spectrum at a resolution of similar to 125,000 has been recorded of molecular hydrogen emission in the reflection nebula NGC 7023, in the S(1) v=1-0 line at 2.121 mu m for a region 5 arcsec in diameter. Th e line is resolved and the derived linewidth corresponds to a kinetic tempe rature of 500+/-70 K, if all motions are thermal. Comparison with data for HI, CI, CII and CO shows that there is a velocity gradient in the molecular material in the photodissociation region, demonstrating the motion of the photodissociation front relative to the molecular cloud. Models of the phot odissociation region experience only limited success in reproducing the kno wn brightness of the H-2 emission in conjunction with the kinetic temperatu re determined here.