Knowledge Bank

A monograph is being prepared on the $NO2$ visible spectrum in the region 5500-6800 \AA . The $NO2$ absorption spectra were photographed on the Argonne National Laboratory 9.1 meter spectrograph with a dispersion of about 0.4 \AA /mm. Positions of approximately 19 000 lines were measured relative to thorium emission standards, using a Grant comparator (National Bureau of Standards, Boulder, Colorado). The reproducibility of unblended lines is about $\pm 0.01cm-1$. It is our intention to present along with microdensitometer tracings, the measured line frequencies $(cm-1)$, wavelengths (\AA), relative intensities, and line-shape appearances. We have also collected the fragmentary portions of the $NO2$ visible spectrum for which line identifications have been made. Of particular interest are the unpublished laser excitation spectra of supersonically cooled $NO2$ molecules, obtained by Smalley, Wharton, and Levy. We also provide an annotated bibliography of about 500 references pertaining to the structural and spectroscopic properties of the $NO2$ molecule. It is hoped that this work will serve as a guide to past studies, as well as to stimulate further studies. The line listings and microdensitometer traces may perhaps even prove useful as a wavelength standard for calibration purposes.