  Mid-infrared molecular line emission detected with the Spitzer Space
Telescope is often interpreted using slab models. However, we need to
understand the mid-infrared line emission in 2D disk models, such that we gain
information about from where the lines are being emitted and under which
conditions, such that we gain information about number densities, temperatures,
and optical depths in both the radial and vertical directions. In this paper,
we introduce a series of 2D thermochemical models of a prototypical T Tauri
protoplanetary disk, in order to examine how sensitive the line-emitting
regions are to changes in the UV and X-ray fluxes, the disk flaring angle, dust
settling, and the dust-to-gas ratio. These all affect the heating of the inner
disk, and thus can affect the mid-infrared spectral lines.
  Using the ProDiMo and FLiTs codes, we produce a series of 2D thermochemical
disk models. We find that there is often a significant difference between the
gas and dust temperatures in the line emitting regions, and we illustrate that
the size of the line emitting regions is relatively robust against changes in
the stellar and disk parameters (namely, the UV and X-ray fluxes, the flaring
angle, and dust settling). These results demonstrate the potential for
localized variations in the line-emitting region to greatly affect the
resulting spectra and line fluxes, and the necessity of allowing for such
variations in our models.
