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.

alyst-substrate adducts and the dihydrides derived from them is the trans disposition of the substrate and diphosphine chelate rings in the former case and the cis disposition in the latter (Figure 9). Unfortunately, all attempts to intercept and examine the dihydride intermediates in these reactions, and thus to probe this theme directly, have thus far been unsuccessful. This failure is consistent with the endothermicity of the H2 oxidative addition step that is a feature of the behavior depicted in Figure 9.Acknowledgment. Support of this research through a grant from the National Science Foundation (CHE 82-17950) and a generous loan of rhodium from Johnson-Matthey Co. are gratefully acknowledged. The NMR facilities used in this research were supported in part through The University of Chicago Cancer Center Grant No. NIH-CA-14599.

up to the moment of reaction. The large reaction distance and small electrostatic contribution in system 3 may thus find an explanation. Of the halogens it appears that only the F~ion has any substantial solvation28 but data for F~substitution are not available to check this interesting correlation between electrolytic and kinetic behavior of ions.The thiosulfate ion is strictly not spherically symmetrical but the double charge may be regarded as "smearing out" any such deviations. This double charge increases r by a factor of 1.2. The effective diameter of the S203-ion is not known

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