Proton tunneling of tropolone in durene single crystal as studied by time-resolved EPR detected excitation spectroscopy

We have measured the excitation spectra for tropolone-OH in durene single c rystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to sep arate the signals due to magnetically different sites. The tunneling double t with 3 cm(-1) was observed in the sharp zero-phonon line. The small split ting indicates that the crystal field increases the barrier of double-minim um potential for the proton tunneling in the S-1 state. Moderately asymmetr ic potentials of the S-0 and S-1 states, where the energetic imbalance betw een two wells in the S-1 state potential is opposite the S-0 state potentia l, reasonably explained the observed unusual intensity ratio of the tunneli ng doublet (0(1)(+) < 0(1)(-)). A well-resolved progression of a phonon ban d with a 15 cm(-1) separation was also obtained in durene crystal at very l ow temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the exci ted state tropolone in durene differed from that of the ground state. (C) 1 999 American Institute of Physics. [S0021-9606(99)00439-0].