Rotation diagrams of HCN lines in the v₁ band detected in MonR2 IRS 3A (panel a) and MonR2 IRS 3B (panel b). The error bars displayed are the 1σ error from the Gaussian fitting, however the error on the column of the R(1) and P(4) lines is estimated from the noise level. Emission lines of which the error is underestimated from the fitting routine due to systematic error in the data reduction process are indicated in grey. These transitions are excluded from the fit used to derive the physical conditions. The column density of the low J lines in MonR21RS 3A is calculated using the integrated line strengths without the contribution from the cloud at 9 km s⁻¹.