C¹⁸O J = 3 → 2 (left panel) and H₂CO J_Ka,Kc = 5_1,5 → 4_1,4 (right panel) line integrated intensity maps (W in K km s^-1) in the 10−11 km s^-1 velocity interval observed with the IRAM 30 m telescope at ~329 GHz and ~351 GHz, respectively (colour scale). Black contours are the Hv = 1 → 0 S(1) emission delineating the H₂ dissociation front (DF, Walmsley et al. 2000). The red contours represent the O i  fluorescent line at 1.32 μm (Walmsley et al. 2000) marking the position of the ionisation front (IF) that separates the H ii region and the neutral cloud. The blue contours represent the H¹³CN J = 1 → 0 emission tracing dense molecular clumps inside the Bar (Lis & Schilke 2003). The target position of the Orion Bar survey, close to the DF, is indicated with a blue circle. The IRAM 30 m beam at 1 mm is plotted in the bottom left corner (black circle).