Zur Deutung des UV.-Spektrums von Pyridin-N-oxid

From measurements of the influence of an electric field on the absorption spectrum of pyridine-N-oxide it is concluded that the 330 nm band is polarized perpendicular to the dipole moment, while the 280 nm transition moment lies parallel. Furthermore from these experiments the dipole moments in both excited states have been determined (Table 1). PARISER -PARR -POPLE -calculations as well as CNDO-calculations admit an assignment of the 330 nm band to an A₁ → B₁, π → π* transition and of the 280 nm band to an A₁ → A₁, π → π* transition. Thereby energy, polarization, intensity of the transition, and the dipole moments of the excited states have been taken into consideration. This assignment does not exclude the possibility of a weak n-π* transition at approximately the same wavelength as the A₁ → B₁ transition.