Knowledge Bank

The gas phase absorption spectrum of $C4N2$ has been measured photoelectrically from 2000 $\backslash AA$ to 1050 $\backslash AA$ with a 1-m monochromator having a 1.0 $\backslash AA$ bandwidth. The region from 1650--1050 $\backslash AA$ is dominated by a $ns\leftarrow \pi$ Rydberg series converging to the first ionization potential at 11.81 eV. Vibrational structure on the short-wavelength side of the Rydberg bands consists of several well-resolved peaks, with an average spacing of $2120cm-1$. This is probably due to excitation of the symmetric $C\equiv N$ stretching mode $\nu 1$ and is very similar to the vibrational structure in the photoelectron spectrum obtained by Baker and $Turner.1$. A non-Rydberg band at 1720 $\backslash AA$ has an oscillator strength of 0.03. The assignment of this band will be discussed with the aid of a simple INDO molecular orbital calculation.