Selected lines of A/E-HCOOCH₃ν_t = 1 (modelled in dark blue) toward Orion-IRc2. The dashed red line and the green continuous line correspond to methyl formate in the ground state and the sum of the emission of v_t = 1 and v_t = 0, respectively. The continuous cyan line corresponds to all lines already modelled in our previous papers except HCOOCH₃ν_t = 0, 1 (see Sect. 5.1). A v_LSR of 9 km s^-1 is assumed. The x-axis is the frequency in GHz.