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Some 69 microwave absorption lines from three isotopic modifications of NO2 have been observed and identified. This spectrum has been completely analyzed in terms of moments of inertia, magnetic fine structure, and centrifugal distortion. The early stages of analysis were complicated by the existence of many mathematical solutions satisfying all of the data then available, but special methods have been developed for treating limited data and selecting the one solution giving the true molecular parameters. The results obtained for 14N16O2 are: Rotational constantsA=239 868.7±11 Mc/secB= 13 000.12±0.6 Mc/secC= 12 303.45±0.6 Mc/secOdd electron expectation values with respect to〈(3r̂a2−1)/2r3〉=−1.73×1024cm−3N−nucleus〈(r̂b−ir̂c)2/r3〉=+3.34×1024cm−3|ψ(0)|2=+3.065×1024cm−3Reduced spin−rotation coupling constantsεaa/A=+0.022563εbb/B=+0.000608εcc/C=−0.007764Force constants from combined microwave−infrared datafd=11.043±0.05  mydn/Åfα= 1.109±0.01fdd=0.481±0.014fdα=2.140±0.05.The magnetic coupling constants are discussed in terms of a simplified electronic structure. The agreement between this structure and the experimental parameters is incomplete, but surprisingly good. Approximate values for the 14N quadrupole coupling constants are obtained.

2C6H6.C26H6Cl8N2O4, benzene-1,2,5,6,7,8-11,12-octachloro-N,N'-dimethylperylene-3 ,4:9,10-bis- (dicarboximide) (Cl8DMP) (2/1), Mr = 850.20, orthorhombic, Pna2(1), a = 23.076 (2), b = 7.2492 (6), c = 20.277 (2) A, V = 3392.0 (8) A3, Z = 4, Dm = 1.69 (1), Dx = 1.665 g cm-3, mu (Mo K alpha, lambda = 0.71073 A) = 7.1 cm-1, F(000) = 1712, T = 297 (1) K, RF = 0.061 for 2134 observed reflections. The structure contains alternating benzene and Cl8DMP molecules stacked along b to form a 2:1 donor-acceptor complex. The Cl8DMP molecule is highly twisted as a result of short intramolecular bay Cl...Cl contacts [3.109 (3), 3.136 (3) A]. The central ring of the perylene fragment is substantially distorted from planarity; internal torsion angles range from 16 (1) to 32 (1) degrees.