The material that formed the present-day Solar System originated in feedingzones in the inner Solar Nebula located at distances within ~20 AU from theSun, known as the planet-forming zone. Meteoritic and cometary material containabundant evidence for the presence of a rich and active chemistry in theplanet-forming zone during the gas-rich phase of Solar System formation. It isa natural conjecture that analogs can be found amoung the zoo of protoplanetarydisks around nearby young stars. The study of the chemistry and dynamics ofplanet formation requires: 1) tracers of dense gas at 100-1000 K and 2) imagingcapabilities of such tracers with 5-100 (0.5-20 AU) milli-arcsec resolution,corresponding to the planet-forming zone at the distance of the closeststar-forming regions. Recognizing that the rich infrared (2-200 micron)molecular spectrum recently discovered to be common in protoplanetary disksrepresents such a tracer, we present a new general raytracing code, RADLite,that is optimized for producing infrared line spectra and images fromaxisymmetric structures. RADLite can consistently deal with a wide range ofvelocity gradients, such as those typical for the inner regions ofprotoplanetary disks. The code is intended as a backend for chemical andexcitation codes, and can rapidly produce spectra of thousands of lines forgrids of models for comparison with observations. Such radiative transfer toolswill be crucial for constraining both the structure and chemistry ofplanet-forming regions, including data from current infrared imagingspectrometers and extending to the Atacama Large Millimeter Array and the nextgeneration of Extremely Large Telescopes, the James Webb Space Telescope andbeyond.
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