THE VACUUM ULTRAVIOLET ABSORPTION SPECTRUM OF DIAZOMETHANE

Abstract

Ultraviolet absorption spectra of CH₂N₂ and CD₂N₂ between 2000 Å and 1350 Å 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 ± 0.001 ev. Examination of a band system at 1900 Å 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 ¹B₁, 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 ¹B₂, in Coriolis interaction with the two ¹B₁ states. Various vibrational bands of this 1900 Å 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, ν₆. There is strong evidence that the molecule remains planar in these excited states.