  Single molecule fluorescence tracking provides information at nm-scale and
ms-temporal resolution about the dynamics and interaction of individual
molecules in a biological environment. While the dynamic behavior of isolated
molecules can be characterized well, the quantitative insight is more limited
when interactions between two indistinguishable molecules occur. We address
here this aspect by developing a solid theoretical foundation for a
spectroscopy of interaction times, i.e. the inference of interaction constants
from imaging data. The non trivial crossover between a power law to an
exponential behavior of the distribution of the interaction times is
highlighted here, together with the dependence of the exponential term upon the
product of the microscopic reaction rates (affinity). Our approach is validated
on simulated as well as experimental datasets.
