Optical transitions to the2B2electronic state region of NO2have been observed in double resonance with three millimeterhyphen;wave ground state rotational transitions. The probed ground state transitions were theN=2 (F1),N=4 (F1), andN=10 (F2),K=0rarr;1Qbranch transitions near 250 GHz. The optical range scanned was 16thinsp;800 to 16thinsp;950 cmminus;1. The 100,10ndash;101,9F2spectrum was combined with previous double resonance results with the ground state 91,9ndash;100,10F1transition. This comparison shows 70 out of 160 upper states withJ=19/2 to have indefinite or mixedNvalues. It establishes violations of the Dgr;N=Dgr;Jselection rule in this spectral region which contains bands with a wide range of spinhyphen;rotation constants. Lack of intensity correlation between the two spectra suggests two classes of upper states are present: a group of stronglyNhyphen;mixed upper states, and a group essentially unmixed inN. Hellerrsquo;sFparameter, which measures the fraction of all possible symmetryhyphen;restricted basis states contributing to a typical eigenstate, is similar for the doublehyphen;resonance spectra of the threeNvalues, but is greater forK=1 than forK=0. By finding upper states in common,Rlines fromN=2 andPlines fromN=4 have been identified.
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