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The UV radiation field is a critical regulator of gas-phase chemistry insurface layers of disks around young stars. In an effort to understand therelationship between photocatalyzing UV radiation fields and gas emissionobserved at infrared and sub-mm wavelengths, we present an analysis of new andarchival HST, Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupuscloud complex and 14 systems in Taurus-Auriga. The HST spectra were used tomeasure LyA and FUV continuum fluxes reaching the disk surface, which areresponsible for dissociating relevant molecular species (e.g. HCN, N2).Semi-forbidden C II] 2325 and UV-fluorescent H2 emission were also measured toconstrain inner disk populations of C+ and vibrationally excited H2. We find asignificant positive correlation between 14 micron HCN emission and fluxes fromthe FUV continuum and C II] 2325, consistent with model predictions requiringN2 photodissociation and carbon ionization to trigger the main CN/HCN formationpathways. We also report significant negative correlations between sub-mm CNemission and both C II] and FUV continuum fluxes, implying that CN is also morereadily dissociated in disks with stronger FUV irradiation. No clearrelationships are detected between either CN or HCN and LyA or UV-H2 emission.This is attributed to the spatial stratification of the various molecularspecies, which span several vertical layers and radii across the inner andouter disk. We expect that future observations with JWST will build on thiswork by enabling more sensitive IR surveys than were possible with Spitzer.

Probing UV-Sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope