The infrared absorption spectrum of the ν3 band of 14NO 2 has been recorded with a resolution and a frequency accuracy much improved over the previous investigations. The K- and N-line assignments have been greatly extended and a more accurate set of spectroscopic constants derived. Several lines in the subbands with Ka ≥ 3 have been observed to be doubled by spin-rotation interaction and spin-rotation interaction constants have been obtained. Several weak series of lines in the spectrum ( Ka = 0, 1, 2, and 3) have been unambiguously assigned to the "hot band" ν2 + ν3 - ν2. Lines of the Ka = 3, 4, 5, and 6 sub-bands of ν3 have been found to be perturbed by a Coriolis interaction with the Ka = 4, 5, 6, and 7 levels of 2 ν2.