  Configuration transitions of individual molecules and atoms on surfaces are
traditionally described with energy barriers and attempt rates using an
Arrhenius law. This approach yields consistent energy barrier values, but also
attempt rates orders of magnitude below expected oscillation frequencies of
particles in the meta-stable state. Moreover, even for identical systems, the
measurements can yield values differing from each other by orders of magnitude.
Using low temperature scanning tunnelling microscopy (STM) to measure an
individual dibutyl-sulfide molecule (DBS) on Au(111), we show that we can avoid
these apparent inconsistencies if we account for the relative position of tip
apex and molecule with accuracy of a fraction of the molecule size. Altering
the tip position on that scale modifies the transition's barrier and attempt
rate in a highly correlated fashion, which on account of the relation between
the latter and entropy results in a single-molecular enthalpy-entropy
compensation. By appropriately positioning the tip apex the STM tip can be used
to select the operating point on the compensation line and modify the
transition rates. The results highlight the need to consider entropy in
transition rates of a single molecule, even at temperatures where entropy
effects are usually neglected.
