AN INVESTIGATION OF THE GEOMETRY AND POLARIZATION OF THE $^{1}B_{3n}, n\Pi^{*}$, EXCITED STATE OF PYRAZINE

Abstract

The lowest excited electronic state of pyrazine (para $C_{4}H_{4}N_{2}$) has been studied both theoretically and spectroscopically in recent years. It’s assignment as an $n\Pi^{*}$ state of $^{1}B_{3u}$ appears to be well established. In the present investigation we are exploring features of transitions involving this state, and the appropriate theoretical description of it. Hartree-Fock and CI calculations have been performed on the $^{1}B_{3u}$ state. These calculation show that the best single configuration description has the excitation strongly localized on a single nitrogen atom at one end of the molecule. Additional studies are being carried out with appropriate multiconfiguration $^{1}B_{3u}$ wave functions to determine whether geometrical distortion from a $D_{2h}$ geometry to a lower $C_{2y}$ symmetry occurs. We will present spectroscopic evidence of our own and of other workers which is consistent with a distortion of the $^{1}B_{3u}$ state to lower symmetry.