THE VACUUM ULTRAVIOLET ABSORPTION SPECTRUM OF DIAZOMETHANE

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.