GHz and 4.593 GHz, respectively, in January 24 to 29, 2019. Also for comparisons, we made repeated observations toward several strong sources (W3IRS5, NGC2024, SgrB2, W33) in our sample. The new results related to those strong sources are consistent with our previous ones. Based on the frequency dependencies of the spectral flux densities in @2013ApJS...204..19, the radio sources 3C123, 3C147, 3C196 and 3C295 were taken as calibrators in our observations. The cross scan mode with a bandwidth of 10 MHz was used for calibrations at 4.829 GHz and 4.593 GHz and the telescope gains are 1.49 Jy K$^{-1}$ and 1.28 Jy K$^{-1}$, respectively. Thus a correction factor of (1.49/1.28) from the different gains at 4.829 GHz and 4.593 GHz should be applied to obtain the accurate value of the isotope abundance ratio (see details in Sect. \[subsec:opticaldepth\]). For C- ($\sim$ 5 GHz) and Ku-band ($\sim$ 14.5 GHz), the sensitivities are both 1.5 Jy K$^{-1}$. The calibrators were observed at suitable elevations of $40\arcdeg-60\arcdeg$, while the elevation range of all the target sources is $20\arcdeg-80\arcdeg$. Beside noise, the uncertainty of the measured flux density is mainly caused by the elevation-dependent gain curve of the TMRT (@2018ITAP..66...2044; see also Sect. \[subsec:opticaldepth\]).

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