Detection of interstellar OH in the far-infrared

Strong absorption lines of OH have been detected at 119.23 and 119.44 ..mu..m in the directon of Sgr B2. The two lines observed arise from the /sup 2/Pi/sub 3/2/, J = 5/2reverse arrow3/2 transitions and imply a column density of N/sub OH/ ..3 transition of NH/sub 3/ at 125 ..mu..m in Sgr B2.