Knowledge Bank

A variety of optical and zf ODMR experiments have been performed on the lowest $(n\Pi \ast )$ triplet states of benzophenone $(BP-h10)$, perdeutero-benzophenone $(BP-h10)$, and -dibromobenzophenone (4,4 -DBBP) in single crystals of $4,4\prime$ -dibromodiphenylether (DDE) at $1.4\circ K$. The data include single-sublevel phosphorescence spectra and amplitude - modulated zf ODHR excitation spectra. The results are analyzed to determine the mechanisms responsible for the population and depopulation of the spin sublevels. A localized model suffices for triplet $BP-h10$ in which the $Tz$ sublevel is moat active. Deuterium substitution has only a small effect on the radiative and nonradiative properties of $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}(n\pi )$ BP. In contrast, bromine substitution has a large and selective effect; this is a consequence of n and $\Pi$; electron delocization. Second-order vibronic contributions are important for the totally symmetric C = O stretching bands in the $4,4\prime$ DBBP phosphorescence spectra.