Probing the Diffuse Interstellar Medium with Observations of Selected Diatomic Molecules: Recent Results from ArH+ and SH

Recent observations of a variety of small molecules, enabled by Herschel and SOFIA, place unique and valuable constraints upon the conditions in the diffuse interstellar medium.  In this teletalk, I will focus on Herschel observations of the recently-discovered argonium (ArH+) molecular ion, which traces material in which the molecular hydrogen fraction is less than 0.1 %; and SOFIA observations of the mercapto (SH) radical, which traces mainly-molecular gas in which the chemistry is modified by the dissipation of turbulence.