We present a study of the abundances and physical conditions in the interstellar gas toward the heavily reddened star HD 192639 [ E _ { ( B - V ) } = 0.64 ] , based on analysis of FUSE and HST /STIS spectra covering the range from 912 to 1361 Å .
This work constitutes a survey of the analyses that can be performed to study the interstellar gas when combining data from different instruments .
Low-velocity ( - 18 to - 8 km s ^ { -1 } ) components are seen primarily for various neutral and singly ionized species such as C i , O i , S i , Mg ii , Cl i , Cl ii , Mn ii , Fe ii and Cu ii .
Numerous lines of H _ { 2 } are present in the FUSE spectra , with a kinetic temperature for the lowest rotational levels T _ { 01 } = ( 90 \pm 10 ) K. Analysis of the C i fine-structure excitation implies an average local density of hydrogen n _ { H } = ( 16 \pm 3 ) cm ^ { -3 } .
The average electron density , derived from five neutral/first ion pairs under the assumption of photoionization equilibrium , is n _ { e } = ( 0.11 \pm 0.02 ) cm ^ { -3 } .
The relatively complex component structure seen in high-resolution spectra of K i and Na i , the relatively low average density , and the measured depletions all suggest that the line of sight contains a number of diffuse clouds , rather than a single dense , translucent cloud .
Comparisons of the fractions of Cl in Cl i and of hydrogen in molecular form suggest a higher molecular fraction , in the region ( s ) where H _ { 2 } is present , than that derived considering the average line of sight .
In general , such comparisons may allow the identification and characterization of translucent portions of such complex lines of sight .
The combined data also show high-velocity components near - 80 km s ^ { -1 } for various species which appear to be predominantly ionized , and may be due to a radiative shock .
A brief overview of the conditions in this gas will be given .