the fraction of the species in unobserved levels) appear to be less. We in general report column densities for  using the CTEX approach based on the integrated intensity of the weakest satellite of (1–0) and for  assuming optically thin conditions. From comparison between the different approaches employed by us, we estimate the column density errors to be 30 percent.

We have also used LVG estimates to infer the density towards the peak and edges of our  map. Here, we assume a temperature of 10 K and have used rates from Green ([@g75]) for collisions of He with . Based on the values in Tab. \[linepar\] (data smoothed to 26 spatial resolution) for the integrated intensities of , we find $n(\MOLH )$ = $4 \times 10^5$  towards the dust peak of L1521F and 2.5$\times$10$^5$  30 North (offset \[-10, 30\]). For (2–1) and (3–2), the corresponding numbers are 6$\times$10$^5$  and 3.5$\times$10$^5$ , at the peak and (-10, 30) offset positions, respectively. These values are similar to the corresponding values for L 1544 consistent with the idea that they have similar density distributions. The density estimates are somewhat smaller than estimates based on the dust emission, probably due to the different (factor of 