HCO⁺ (10) spectra obtained from RATRAN modeling of a collapsing cloud (see text). The observed HCO⁺ (10) spectrum is plotted in black, and the position of the spectrum is shown in columnd 2 and 3 of Table 5. The dashed green line is the spectrum obtained by the RATRAN model, and the green line is the result of Gaussian fitting of HCO⁺ (10). The dashed red line indicates the central radial velocity of H¹³CO⁺.