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The relative abundances of singly-deuterated methanol isotopologues,[CH$_{2}$DOH]/[CH$_{3}$OD], in star-forming regions deviate from thestatistically expected ratio of 3. In Orion KL, the nearest high-massstar-forming region to Earth, the singly-deuterated methanol ratio is about 1,and the cause for this observation has been explored through theory for nearlythree decades. We present high-angular resolution observations of Orion KLusing the Atacama Large Millimeter/submillimeter Array to map small-scalechanges in CH$_{3}$OD column density across the nebula, which provide a newavenue to examine the deuterium chemistry during star and planet formation. Byconsidering how CH$_{3}$OD column densities vary with temperature, we findevidence of chemical processes that can significantly alter the observed columndensities. The astronomical data are compared with existing theoretical workand support D-H exchange between CH$_{3}$OH and heavy water (i.e., HDO andD$_{2}$O) at methanol's hydroxyl site in the icy mantles of dust grains. Theenhanced CH$_{3}$OD column densities are localized to the Hot Core-SW region, apattern that may be linked to the coupled evolution of ice mantel chemistry andstar formation in giant molecular clouds. This work provides new perspectiveson deuterated methanol chemistry in Orion KL and informs considerations thatmay guide future theoretical, experimental, and observational work.

On the Relationship between CH$_3$OD Abundance and Temperature in the Orion KL Nebula