Vacuum ultraviolet spectroscopy of cyanogen and cyanoacetylenes

Abstract

The vapor phase absorption spectra of cyanogen, cyanoacetylene, dicyanoacetylene, and dicyanodiacetylene have been recorded between 2000 and 1050 Å. Substantial perturbations in the intensity and positions of particular bands upon the addition of helium at 1500 psi pressure served to identify several Rydberg series. These series are assigned on the basis of their quantum defects and symmetry considerations. CNDO/2‐CI calculations were used to interpret the valence shell transitions. A very intense intravalence shell band, assigned as a ${}^1{\Sigma }_u^{+}{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{\Sigma }_g^{+}$ system arising from the lowest π→π* configuration, dominates the spectra of all the molecules. A moderately intense intravalence shell band, assigned as a ${}^1{\Pi }_u{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{\Sigma }_g^{+}$ transition arising from the lowest n→π* configuration further characterizes the spectra.