We present an analysis of interstellar H _ { 2 } toward HD 37903 , which is a hot , B 1.5 V star located in the NGC 2023 reflection nebula .
Meyer et al . ( 2010 ) have used a rich spectrum of vibrationally excited H _ { 2 } observed by the HST to calculate a model of the interstellar cloud toward HD 37903 .
We extend Mayer ’ s analysis by including the \nu ” =0 vibrational level observed by the FUSE satellite .

The T _ { 01 } temperature should not be interpreted as a rotational temperature , but rather as a temperature of thermal equilibrium between the ortho and para H _ { 2 } .
The ortho to para H _ { 2 } ratio is lower for the lowest rotational levels than for the higher levels populated by fluorescence .
The PDR model of the cloud located in front of HD 37903 points to a gas temperature T _ { kin } =110–377 K , hydrogen density n _ { H } =1874–544 cm ^ { -3 } and the star–cloud distance of 0.45 pc .