  We examine changes in the molecular abundances resulting from increased
heating due to a self-luminous planetary companion embedded within a narrow
circumstellar disk gap. Using 3D models that include stellar and planetary
irradiation, we find that luminous young planets locally heat up the parent
circumstellar disk by many tens of Kelvin, resulting in efficient thermal
desorption of molecular species that are otherwise locally frozen out.
Furthermore, the heating is deposited over large regions of the disk, $\pm5$ AU
radially and spanning $\lesssim60^\circ$ azimuthally. From the 3D chemical
models, we compute rotational line emission models and full ALMA simulations,
and find that the chemical signatures of the young planet are detectable as
chemical asymmetries in $\sim10h$ observations. HCN and its isotopologues are
particularly clear tracers of planetary heating for the models considered here,
and emission from multiple transitions of the same species is detectable, which
encodes temperature information in addition to possible velocity information
from the spectra itself. We find submillimeter molecular emission will be a
useful tool to study gas giant planet formation in situ, especially beyond
$R\gtrsim10$ AU.
