Knowledge Bank

A detailed rotational analysis of the (0,0) band of the $22B2-X~2A1$ electronic transition of $NO2$, at 2491 {\AA}, has been carried out. Although the lines are slightly broadened as a result of predissociation, it has been possible to determine the five quartic centrifugal distortion constants and the spin-rotation coupling constant $ϵaa$ for the upper state. The centrifugal distortion constants allow the position of the unseen vibrational level $\nu 3\prime$ to be estimated: the results offer no support to the suggestion of Coon, Cesani, and Huberman (J. Chem. Phys. 52, 1647 (1970)) that there is a double minimum potential function in the antisymmetric stretching coordinate of the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B2$ state. The geometric structure of the zero-point level of the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B2$ state is $r(N-O)=1.3142$ {\AA}, $\angle ONO=120.87\circ$, and its lifetime (as calculated from the linewidths) is $42\pm 5$ ps.