THE METHOD OF 'MAGNETO-PHOTOSELECTION' OF THE LOWEST EXCITED TRIPLET STATE OF AROMATIC MOLECULES.

The unique intensity distribution as a function of the angles between the principal magnetic axes and the applied magnetic field of the delta m or -1 ESR transitions of a collection of randomly oriented photo-excited triplet state molecules has been used as a magneto selection device to observe only the molecules whose principal magnetic axes are parallel to the magnetic field. The latter is possible because the shape of the derivative of the delta m or -1 ESR derivative curve gives special prominence to those resonant fields corresponding to transitions of molecules processing a canonical orientation. Changes in the relative intensities of the derivating ESR lines of the magneto-photoselected collection of molecules were observed as a function of the angle between the external field and the polarization direction of the exciting monochromatic light. The results obtained for glasses containing naphthalene-d8 or quinoxaline are analyzed in terms of the known ESR spectra and polarization of the electronic absorption bands the conclusions agree very well with theoretical predictions. The known directions of polarization of the electronic absorption bands of phenanthrene-d10 were then used to assign the delta m or -1 ESR spectrum of phenanthrene-d10 in EPA glass at 77 K. The assignment is found to agree with the first order spectrum calculated using the published D and E values determined from single crystal studies. Author