Experimental studies [Hauser, M. J. B.; Olsen, L. F.
J.
Chem. Soc., Faraday Trans.
1996,
92, 2857−2863]
of the peroxidase−oxidase (PO) reaction at pH values in excess of 5.4
suggest the existence of narrow regions
of complex dynamics between adjacent mixed-mode oscillations (MMOs)
that occur in period-adding sequences.
Previously [Hauser, M. J. B.; Olsen, L. F.; Bronnikova, T. V.;
Schaffer, W. M. J. Phys. Chem. B
1997,
101,
5075−5083], it was argued that both the period-adding sequences and
the transitional regions between
neighboring MMOs are predictable by a detailed model of the reaction
called BFSO [Bronnikova, T. V.;
Fed'kina, V. R.; Schaffer, W. M.; Olsen, L. F. J. Phys.
Chem.
1995, 99, 9309−9312]. In the
present paper,
we study the transitional regions via computer simulation. Our
investigations indicate that the motion therein
may be periodic, quasiperiodic, or chaotic. In greater detail, we
observe a quasiperiodic route to chaos whereby
period-doubled cycles give rise to doubled tori that, in turn, undergo
homoclinic bifurcations to chaos. Because
the latter transitions are a consequence of progressive fattening of
the tori, we propose calling this scenario
the “fat torus” route to chaos, and the homoclinic bifurcations
“fat torus” bifurcations (FTBs). The numerical
results are qualitatively consistent with the experimental findings
reported to date. FTBs and the resultant
period-doubled, fractal tori may provide a criterion for discriminating
among alternative models of the PO
reaction.