PACS rotationally excited OH J = 7/2    →    5/2 lines at  ~84 μm (E_u/k = 291 K) overlaid on the distribution of the CO J = 6–5 peak brightness temperature (colour image) observed with the CSO telescope at  ~11′′ resolution (Lis et al. 1998). White contours show the brightest regions of Hv = 1–0 S(1) emission (Walmsley et al. 2000). Lower intensity H extended emission is present in the entire field (van der Werf et al. 1996). Violet stars shows the position of the H¹³CN J = 1–0 clumps deeper inside the Bar (Lis & Schilke 2003). Note the decrease of OH line intensity with distance from the ionization front.