Formaldehyde absorption at 6 cm has been mapped in the prominent dust lane which separates the optical nebulae IC 1318 b and c. The apparent optical depths of H 2 CO range between 0.2 and 0.8 within the dust lane and at most ~0.1 where the visual absorption falls below ~4 to 4.5 mag. However, there is not a detailed correlation between the observed H 2 CO absorption and the dust. In the region of highest visual extinction, the 6 cm absorption is reduced, but here 2 mm emission from more highly excited levels of H 2 CO is observed instead.It is concluded that the H n regions are physically associated with the dust and molecules. The (LSR) radial velocities of the H 2 CO absorption are similar to those of the Ha emission with the most negative values in the regions of least obscuration, which suggests that the H n regions may be expanding into the molecular cloud.

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