The FUSE far-ultraviolet interstellar spectra toward seven targets in \object NGC 6231 show that the molecules H _ { 2 } , HD , and CO as well as various atomic species are distributed in several clouds .
The main absorption component found on the sight lines lies in the Lupus cloud region at a distance of about 150 pc , and there is a weaker second one , presumably in the \object Sco OB1 shell surrounding \object NGC 6231 ( d \simeq 1.8 kpc ) .
H _ { 2 } excitation modelling is used to constrain the radiation field and the density in the gas ; HD is used to estimate the abundance of H ^ { + } .
The small angular separation of the target stars allows column density variations to be probed over the field of view , on scales of 0.05 pc in the case of the Lupus cloud distance .
They are 40 \% for H _ { 2 } and 60 \% for \ion Hi .
A rather strong radiation field inside the molecular clouds suggests a separation of the gas into smaller cloudlets also along the line of sight .