Using intracavity laser absorption spectroscopy combined with a supersonic slit jet, we have observed and analyzed seven vibronic cold bands of NO2 between 10 800 and 11 680 cm(-1). The vibronic energies, relative intensities, A, B, and C rotational constants, and the spin-rotation constants have been determined. The rotational constants play a crucial role in the vibronic assignments. The seven observed states are vibronically mixed. However, three of them have a dominant (A) over tilde B-2(2) electronic character while the four others have a dominant (X) over tilde (2)A(1) character. The vibrational assignments and energies of the three (A) over tilde B-2(2) levels are: (1, 0, 0) at 10 999.42 cm(-1), (0, 2, 0) at 11 210.50 cm(-1), and (0, 0, 2) at 11 283.15 cm(-1). The frequencies of the symmetric stretch, (omega(1)congruent to1265 cm(-1)), and bending, (omega(2)congruent to738 cm(-1)) modes derived from the (1, 0, 0) and (0, 2, 0) levels are in agreement with ab initio calculations. In contrast, the frequency of the antisymmetric stretch, omega(3)congruent to775 cm(-1), derived from the observed (0, 0, 2) level, agrees only with the ab initio value obtained by Kaldor while other ab initio values ranging from 390 to 1750 cm(-1) were reported. The four levels with a dominant (X) over tilde (2)A(1) character have been tentatively vibrationally assigned. The present experimental data allows for a first experimental determination of the two (A) over tilde B-2(2) stretch vibrational frequencies which are necessary to model the (X) over tilde (2)A(1)-(A) over tilde B-2(2) vibronic interactions, i.e., the conical intersection between (X) over tilde (2)A(1) and (A) over tilde B-2(2) potential energy surfaces. (C) 2003 American Institute of Physics.