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It is increasingly recognized that the integrity of the data input is one of the most serious limiting factors in modeling complex chemical systems. The reliability of the results generated in modeling studies is critical considering their application to environmental regulation and control. The purpose of this workshop was to bring together modelers, chemical kineticists, theoreticians and program managers, in order to define the critical data needs for modeling the troposphere. This collection of review papers, comments, and recommendations should serve a wide community of atmospheric scientists in identifying and attacking priority problem areas. The National Bureau of Standards is pleased to be responsible for this publication, and to have joined with the Environmental Protection Agency as cosponsors of the workshop.

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.

The J0→1 and J1→2 a-type transitions of CH3NCO and CD3NCO have been studied. These transitions are complicated by the population of a number of internal rotation states. Several absorptions arising from the lowest energy internal rotation states have been assigned. The barrier to internal rotation of the methyl group in CH3NCO has been found to be 49±3 cal/mole from the splitting of the J3→4, K=±1, m=±3 transition by the barrier. The component of electric dipole moment parallel to the a axis has been found to be 2.81±0.06 D by measurement of the Stark effect. The nitrogen quadrupole coupling constant has been found to be eqQ=+2.3 Mc/sec.

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