  We study reheating in $\alpha$-attractor models of inflation in which the
inflaton couples to other scalars or fermions. We show that the parameter space
contains viable regions in which the inflaton couplings to radiation can be
determined from the properties of CMB temperature fluctuations, in particular
the spectral index. This may be the only way to measure these fundamental
microphysical parameters, which shaped the universe by setting the initial
temperature of the hot big bang and contain important information about the
embedding of a given model of inflation into a more fundamental theory of
physics. The method can be applied to other models of single field inflation.
