Knowledge Bank

Ultraviolet absorption spectra of $CH2N2$ and $CD2N2$ between 2000 {\AA} and 1350 {\AA} have been photographed. Many electronic transitions occur in this region, including a Rydberg series (first reported by Herzberg) which gives the first I.P. of diazomethane as $8.999\pm 0.001$ eV. Examination of a band system at 1900 {\AA} has shown that it contains three close-lying electronic transitions, with origins within $200cm-1$. Of the upper states, the two outermost, D and F, are shown by rotational analysis to be of the same symmetry species $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}B1$, while the third, E, lying between them, seems to be responsible for large perturbations observed in the K-structures. By inference, this third state must be $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B2$, in Coriolis interaction with the two $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}B1$ states. Various vibrational bands of this 1900 {\AA} group have been assigned; among these are a number of vibrationally-forbidden bands involving one and three quanta of the out-of-plane $CH2$ bending frequency, $\nu 6$. There is strong evidence that the molecule remains planar in these excited states.