[en] The very weak 3ν_1+3ν_2+ν_3 absorption band of the main isotopologue of nitrogen dioxide, "1"4N"1"6O_2, is investigated for the first time near 7587 cm"−"1. The absorption spectrum was recorded by high sensitivity Continuous Wave-Cavity Ring Down Spectroscopy with a noise equivalent absorption of α_m_i_n≈1×10"−"1"0 cm"−"1. 414 lines of the 3ν_1+3ν_2+ν_3 band were assigned with rotational quantum numbers N and K_a as high as 32 and 6, respectively, what corresponds to 518 rotation–vibration transitions. The overall set of spin–rotation energy levels was modeled in the frame of the effective Hamiltonian approach and reproduced with an RMS of 6×10"−"3 cm"−"1 for the (obs.–calc.) deviations. The effective Hamiltonian includes interactions with three nearby dark states – (350), (062) and (312) – in Coriolis interaction with the (331) bright state. Using a selected set of experimental line intensities and the fitted values of the vibration–rotation Hamiltonian parameters, the principal parameter in the dipole moment operator expansion is determined for the 3ν_1+3ν_2+ν_3 band. With maximum line intensity on the order of 2.5×10"−"2"7 cm/molecule at 296 K, the 3ν_1+3ν_2+ν_3 band is the weakest band of the NO_2 molecule rovibrationnally assigned so far. - Highlights: • First detection and analysis of the 3ν_1+3ν_2+ν_3 band of NO_2 near 7587 cm"−"1. • 414 lines were assigned with rotational quantum numbers N and K_a up to 32 and 6. • Effective Hamiltonian modeling. • Coriolis resonance coupling with three dark states: (350), (062) and (312). • The 3ν_1+3ν_2+ν_3 band is the weakest NO_2 band rovibrationnally assigned so far.