that of molecular nitrogen such as N$_{2}$H$^{+}$ and NH$_{3}$ (as well as their deuterated counterparts) do not condense out in the same fashion and hence can be used as tracers of the dense gas (Bergin & Langer [@bl97]). The extent to which this is true is debatable but it is a useful hypothesis and substantiated by the general similarity of the spatial distributions seen for example in dust emission and in maps of (Tafalla et al. [@taf02],  [@tmc03]).\
Caselli et al. ([@cas02a],[@cas02b]) have used  and  to derive the physical, chemical and kinematical properties of L1544. They found that L1544 has a central  column density of $1.5 \times 10^{13}$ cm$^{-2}$ and a column density ratio $N(\NTDP )/N(\NTHP )$ of 0.24. The  linewidths towards the nucleus (the dust emission peak) are roughly 0.3 km s$^{-1}$ and decrease as one goes to positions away from the center. The line of sight velocity measured in (1-0) and (2-1) shows a gradient along the minor axis of the elliptical structure seen in 1.3mm dust emission but no clear gradient along the major axis.

In this paper, we will study another core in the Taurus complex, L1521F (at an assumed distance of 140 parsec) using the 