Science with an ngVLA: Deuteration in starless and prestellar cores

In dense starless and protostellar cores, the relative abundance of deuterated species to their non-deuterated counterparts can become orders of magnitude greater than in the local interstellar medium. This enhancement proceeds through multiple pathways in the gas phase and on dust grains, where the chemistry is strongly dependent on the physical conditions. In this Chapter, we discuss how sensitive, high resolution observations with the ngVLA of emission from deuterated molecules will trace both the dense gas structure and kinematics on the compact physical scales required to track the gravitational collapse of star-forming cores and the subsequent formation of young protostars and circumstellar accretion regions. Simultaneously, such observations will play a critical role in tracing the chemical history throughout the various phases of star and planet formation. Many low-J transitions of key deuterated species, along with their undeuterated counterparts, lie within the 60-110 GHz frequency window, the lower end of which is largely unavailable with current facilities and instrumentation. The combination of sensitivity and angular resolution provided only by the ngVLA will enable unparalleled detailed studies of the physics and chemistry of the earliest stages of star formation.