Microwave-optical double resonance in NO2

A series of experiments performed to establish the nature of the previously reported microwave optical double resonance signals in electronically excited nitrogen dioxide are reported. The DC stark effect, hyperfine spectrum, and microwave saturation behavior of the double resonance signals observed by exciting NO₂ with the 4880 Å line of an argon ion laser have been studied. The data presented support the assignment of this double resonance signal as occurring within the rovibronic manifold of the ²B₂ electronic state. The observation of a number of new excited state microwave transitions is also reported.