A Multi-Wavelength Perspective of Volatiles Across Protoplanetary Disk Regions

Abstract

This thesis investigates the spatial distribution, excitation, and chemical evolution of volatiles in protoplanetary disks through a combination of submillimeter interferometry and mid-infrared spectroscopy. Leveraging high-resolution ALMA observations and recent JWST-MIRI data, we characterize how the molecular composition varies across disk regions and with disk properties. The work aims to constrain both physical conditions and chemical processes relevant to planet formation, with particular focus on deuterium fractionation, snowline physics and chemistry, and the role of pebble drift in enriching inner disk gas. In Chapter 2 we carry out multi-line ALMA observations of deuterated organics in TW Hya, demonstrating that \textit{in-situ} deuterium fractionation occurs near the CO snow-surface, consistent with H2D+-driven chemistry. In Chapter 3, we perform JWST-MIRI spectroscopy of the AS 209 disk, revealing rich water and organic emission, with notable temporal variability relative to archival Spitzer data. In Chapter 4, we develop a retrieval framework for inferring radial water vapor distributions from unresolved JWST spectra, finding that the observable cold water masses anti-correlate with disk size, likely due to efficient icy pebble drift. In Chapter 5, we analyze the transition disk GM Aur with JWST, where volatile depletion in the inner-disk is accompanied by strong OH emission from photodissociation, pointing to irradiation-driven chemical evolution. Finally, in Chapter 6 we extend the prior analyses to a 40-disk sample from the IDECO JWST survey, confirming and revealing new links between disk structure, stellar properties, and water vapor emission. Together, these studies provide new empirical constraints on how volatile chemistry in disks is actively reshaped by local thermodynamic conditions, dynamics, and stellar irradiation.