ADIABATIC PASSAGE THROUGH AN AVOIDED CROSSING

Fast magnetic field sweeps (approximately 5 x 10(8) G s-1) are used for passage through an avoided crossing in the photoexcited triplet state of pentacene in p-terphenyl crystals. When B0parallel-tox (molecular long axis), there is a level crossing calculated to be near 143 G. Our experiments reveal that the crossing is an avoided one, and the passage through the crossing is adiabatic. Our findings are consistent with the Landau-Zener-Stueckelberg theory of passage through an avoided crossing. By applying radio frequency pulses in the neighborhood of the avoided crossing we estimate the magnitude of the energy gap: 25 +/- 8 MHz.