Knowledge Bank

Rotationally resolved spectra of eight bands within $200cm-1$ of the $S1$ origin of 4-dimethylaminobenzonitrile (DMABN) have been obtained. These bands have previously been assigned, at vibrational resolution, as progessions involving the inversion and torsional coordinates of the dimethylamino $group.2$ At rotational resolution each band exhibits perpendicular-type structure, principally b type. All bands have been fit with a near-prolate symmetric top Hamiltonian, yielding the inertial parameters of the connected vibrational levels accurate to $\pm 0.1MHz$. This information, together with the results of theoretical calculations, is then used to speculate about the geometry of DMABN in its $S0$ and $S1$ states, and how it changes along the two low frequency coordinates. Implications of these results for the presumed twisted internal charge transfer character of $S1$ DMABN3 also will be discussed