  The photoisomerization reaction of the retinal chromophore in rhodopsin was
computationally studied using a two-state two-mode model coupled to thermal
baths. Reaction quantum yields at the steady state (10 ps and beyond) were
found to be considerably different than their transient values, suggesting a
weak correlation between transient and steady-state dynamics in these systems.
Significantly, the steady-state quantum yield was highly sensitive to minute
changes in system parameters, while transient dynamics was nearly unaffected.
Correlation of such sensitivity with standard level spacing statistics of the
nonadiabatic vibronic system suggests a possible origin in quantum chaos. The
feasibility of experimental observation of this phenomenon and its implications
in condensed-phase photochemistry and biological light sensing are discussed.
