0.08\
DR21 & 15.2 & -4.208 $\pm$ 0.018 & 3.74 & -2.61 & -0.0786 $\pm$ 0.019 & 2.06 & -2.42 & 3.5 & -2.05 & 0.6\
J205658.56 & 0.13 & -0.71 $\pm$ 0.015 & 3.29 & 0.84 & -0.037 $\pm$ 0.013 & 1.81 & 1.13 & $<0.1$ & -0.25 & $>0.09$\
J205703.98 & 0.06 & -0.804 $\pm$ 0.014 & 3.05 & 1.15 & -0.041 $\pm$ 0.012 & 1.28 & 1.13 & - & -0.15 & -\

Data reduction and Results {#sec:DataReduction}
==========================

Optical Depth and Column Density {#subsec:opticaldepth}
--------------------------------

We used the GILDAS/CLASS package to reduce the spectral line data. A first order polynomial was subtracted from each spectrum for baseline removal. Then we obtained the line parameters via Gaussian fitting for those 38 sources, which are presented in Table \[Table1\]. The spectra of the $2_{11}-2_{12}$ lines of H$_2$$^{12}$CO, as well as the $1_{10}-1_{11}$ lines of H$_2$$^{12}$CO and H$_2$$^{13}$CO, after subtracting baselines and applying Hanning smoothing, are shown in Figure \[fig1\]. For those 46 sources with only a detection of the H$_2$CO $1_{10}-1_{11}$ line, spectra and line parameters derived from Gaussian fitting are presented in Appendices \[B\] and \[C\], respectively.

![image](1.eps){width="233pt"} ![image](2.eps){width="233pt"} ![image](3.eps){width="233pt"} ![image](4.eps){width="233pt"} ![image](5.eps){width="233pt"} ![image](6.eps){width="233pt"} ![image](7.eps){width="233pt"} ![image](8.eps){width="233pt"} ![image](9.eps){width="233pt"} ![image](10.eps){width="233pt"}

