  The material that formed the present-day Solar System originated in feeding
zones in the inner Solar Nebula located at distances within ~20 AU from the
Sun, known as the planet-forming zone. Meteoritic and cometary material contain
abundant evidence for the presence of a rich and active chemistry in the
planet-forming zone during the gas-rich phase of Solar System formation. It is
a natural conjecture that analogs can be found amoung the zoo of protoplanetary
disks around nearby young stars. The study of the chemistry and dynamics of
planet formation requires: 1) tracers of dense gas at 100-1000 K and 2) imaging
capabilities of such tracers with 5-100 (0.5-20 AU) milli-arcsec resolution,
corresponding to the planet-forming zone at the distance of the closest
star-forming regions. Recognizing that the rich infrared (2-200 micron)
molecular spectrum recently discovered to be common in protoplanetary disks
represents such a tracer, we present a new general raytracing code, RADLite,
that is optimized for producing infrared line spectra and images from
axisymmetric structures. RADLite can consistently deal with a wide range of
velocity gradients, such as those typical for the inner regions of
protoplanetary disks. The code is intended as a backend for chemical and
excitation codes, and can rapidly produce spectra of thousands of lines for
grids of models for comparison with observations. Such radiative transfer tools
will be crucial for constraining both the structure and chemistry of
planet-forming regions, including data from current infrared imaging
spectrometers and extending to the Atacama Large Millimeter Array and the next
generation of Extremely Large Telescopes, the James Webb Space Telescope and
beyond.
