  There is no unique way to quantify the degree of delocalization of quantum
states in unbounded continuous spaces. In this work, we explore a recently
introduced localization measure that quantifies the portion of the classical
phase space occupied by a quantum state. The measure is based on the
$\alpha$-moments of the Husimi function and is known as the R\'enyi occupation
of order $\alpha$. With this quantity and random pure states, we find a general
expression to identify states that are maximally delocalized in phase space.
Using this expression and the Dicke model, which is an interacting spin-boson
model with an unbounded four-dimensional phase space, we show that the R\'enyi
occupations with $\alpha>1$ are highly effective at revealing quantum scars.
Furthermore, by analyzing the high moments ($\alpha>1$) of the Husimi function,
we are able to identify qualitatively and quantitatively the unstable periodic
orbits that scar some of the eigenstates of the model.
