Knowledge Bank

While testing a wavelength calbration system for molecular beam work in the visible region we have measured the hyperfine structures of the $K=0$ bands at 593.5 nm and 585.1 mi In the spectrum of jet-cooled $NO2$ (bands 99 and 115 of Smalley $etal.1$). Linewidths of 10 MHz were obtained typically: for the strongest lines these could be reduced to 2 MHz by a Lamb-dip technique to resolve closely spaced components. The calibration system allowed the hyperf ins splittings of a rotational line to be measured to $\pm 1MHz$, while giving agreement to $\pm 10MHz$ between $\Delta 2F\prime \prime (N)$ combitiation differences measured from the optical spectrum and calculated from the microwave spectrum. The N. J.and F assignments could then be made unambiguously without the need for wavelength-resolved fluorescence. Values for the electron spin-rotation, Fermi contact and (1.5) dipolar parameters were obtained for the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B2$ upper levels with $N=1,3,\dots 9$. Good agreement was obtained with literature $values2$ where they exist. We find that the spectrum in this region consists of individual subbands which can each be approximately described by a single set of constants, though the density of local perturbations requires that the structure of each N' level be treated separately. It seems that the apparently contradicting descriptions of the spectrum given by Lehmann $etal.3$ and Demtroder $etal.2$ are not Inconsistent with each other, but represent different viewpoints of the same perturbed system.