  Lifetimes of complexes formed during helium-hydrocarbon collisions at low
temperature are estimated for symmetric top hydrocarbons. The lifetimes are
obtained using a density-of-states approach. In general the lifetimes are less
than 10-100 ns, and are found to decrease with increasing hydrocarbon size.
This suggests that clustering will not limit precision spectroscopy in helium
buffer gas experiments. Lifetimes are computed for noble-gas benzene collisions
and are found to be in reasonable agreement with lifetimes obtained from
classical trajectories as reported by Cui {\it et al}.
