  The pre-transitional disk around the Herbig Ae star HD 169142 shows a complex
structure of possible ongoing planet formation in dust thermal emission from
the near infrared (IR) to millimeter wavelength range. Also, a distinct set of
broad emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 $\mu$m, commonly
attributed to polycyclic aromatic hydrocarbons (PAHs), are detected prominently
in the HD 169142 disk. We model the spectral energy distribution (SED) as well
as the PAH emission features of the HD 169142 disk simultaneously with porous
dust and astronomical-PAHs taking into account the spatially resolved disk
structure. Our porous dust model consisting of three distinct components that
are primarily concentrated in the inner ring, middle ring, and outer disk,
respectively, provides an excellent fit to the entire SED, and the PAH model
closely reproduces the observed PAH features. The accretion of ice mantles onto
porous dust aggregates occurs between ~16 AU and 60 AU, which overlaps with the
spatial extent (~50 AU) of the observed PAH emission features. Finally, we
discuss the role of PAHs in the formation of planets possibly taking place in
the HD 169142 system.
