THE VACUUM ULTRAVIOLET ABSORPTION SPECTRUM OF DIAZOMETHANE

Abstract

Ultraviolet absorption spectra of $CH_{2}N_{2}$ and $CD_{2}N_{2}$ 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 $200 cm^{-1}$. Of the upper states, the two outermost, D and F, are shown by rotational analysis to be of the same symmetry species $^{1}B_{1}$, 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 $^{2}B_{2}$, in Coriolis interaction with the two $^{1}B_{1}$ 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 $CH_{2}$ bending frequency, $\nu_{6}$. There is strong evidence that the molecule remains planar in these excited states.