Reaction rates for fluctuating barriers with asymmetric noise

Thermally activated escape over a high barrier fluctuating randomly in time is investigated for asymmetric flipping rates. By means of the Fokker-Plan ck approach approximate methods developed for symmetric noise are applied t o calculate the relaxation eigenvector and ultimate relaxation rate for pie cewise linear potentials in the Smoluchowski limit. The ranges of validity of these approaches are discussed. Furthermore, the exact result for weak t hermal noise but arbitrary barrier flipping rates is derived and its depend ence on the asymmetry studied in detail. (C) 1999 American Institute of Phy sics. [S0021-9606(99)51235-X].