Knowledge Bank

The 7000 \AA and 3500 \AA absorption systems in azulene $(C10H8)$ have been studied in some detail and correlated with polarized infra-red measurements. The system is weak, diffuse and polarized along the short molecular axis; the 75 bands observed in the vapour are attributed to 7 totally symmetric fundamental vibrations. The second system (long-axis polarized) is both stronger and sharper. Of 180 vapour bands, 85% are assigned using 11 upper state vibrations, some or them short-axis polarized, and 5 low difference frequencies which are provisionally identified. Various fluorescence and condensed-phase absorption studies were also made. The observations appear to confirm Pariser’s and Moffitt’s predictions concerning the nature of the excited states.