High-Resolution Electronic Absorption Spectra of Diazanaphthalenes in the Vapor Phase

The absorption spectrum of quinoxaline vapor for $\text{λ\hspace{0.17em}>\hspace{0.17em}2000 Å}$ is presented. Two diffuse $\mathrm{\pi *\hspace{0.17em}\leftarrow \hspace{0.17em}\pi }$ systems and a single sharp $\mathrm{\pi *\hspace{0.17em}\leftarrow \hspace{0.17em}n}$ system are observed. A vibrational analysis of observed broad and sharp bands is given for the allowed ${}^1{B}_1{\mathrm{(n\pi *)\hspace{0.17em}\leftarrow \hspace{0.17em}}}^1{A}_1$ electronic system, and a 0–0 band is assigned at 27 071 cm⁻¹. Characteristic band contours and correlation with low‐temperature polarization data allow the assignment of nine fundamental vibrations in the electronic excited state. Six ground electronic state fundamental vibrations are also assigned. The observed band contours and prominent frequencies of quinoxaline are compared with other diazanaphthalenes, and new spectral data for quinazoline and cinnoline are presented.