of our sample are listed in Appendix \[A\].

Among our 112 targets, 84 sources were successfully detected in the $1_{10}-1_{11}$ line of H$_2$CO, and 38 sources of these 84 were also successfully detected in the $1_{10}-1_{11}$ line of H$_2$$^{13}$CO. Subsequently we observed the $2_{11}-2_{12}$ lines of H$_2$CO for these 38 sources and all were detected. 5 sources are showing two velocity components. Thus, 43 radial velocity components were detected towards these 38 sources. The Signal-to-Noise (S/N) ratios of the $1_{10}-1_{11}$ line of H$_2$CO are greater than 25 for these 38 sources. For the $1_{10}-1_{11}$ line of H$_2$$^{13}$CO and the $2_{11}-2_{12}$ line of H$_2$CO, the corresponding S/N ratios are greater than 5. To determine apparent optical depths, complementary observations for their continuum at both C- and Ku-bands were performed toward those 38 sources, from 2017 October 26 to November 4 and during 2018 February 4 to 8. We used the C- and Ku-band receivers, centered at 4.829660 GHz and 14.48848 GHz with 500 MHz bandwidth, respectively. A cross-scan mode was used for observations, where the antenna beam pattern was driven repeatedly in right ascension (RA) and declination (Dec) over the source position. The data were acquired with the DIBAS backend system. 