  We report new analyses of spectra of the $3.2-3.3~\mu$m absorption feature
observed in the diffuse interstellar medium toward three Milky Way sources:
2MASS $J17470898-2829561$ (2M1747) and the Quintuplet Cluster, both located in
the Galactic center, and Cygnus OB2-12. The $3.2-3.3~\mu$m interval coincides
with the CH-stretching region for compact polycyclic aromatic hydrocarbons
(PAHs). We focus on the 2M1747 spectrum. Its published optical depth spectrum
contains residual telluric transmission features, which arise from the 0.06
difference in mean airmasses between the observations of the source and its
telluric standard star. We corrected the published spectrum by adding the
airmass residual optical depth spectrum. The corrected spectrum is well fit by
a superposition of four Gaussians. The absorption spectra of the other two
sources were also fit by four Gaussians, with similar central wavelengths,
widths, and relative peak opacities. We associate the three longer wavelength
Gaussians covering the $3.23-3.31~\mu$m interval with compact PAHs in positive,
neutral, and negative charge states. We identify the shortest wavelength
Gaussian, near 3.21 $\mu$m, with irregularly-shaped PAHs. Constraints imposed
by spectral smoothness on the corrected 2M1747 spectrum, augmented by a PAH
cluster formation model for post-asymptotic giant branch stars, suggests that
$> 99$\%\ of the PAHs in the diffuse interstellar medium reside in small
clusters. This study supports the PAH hypothesis, and suggests that a family of
primarily compact PAHs with a C$_{66}$H$_{20}$ (circumvalene) parent is
consistent with the observed mid-infrared and ultraviolet interstellar
absorption spectrum.
