  Non-radiative energy transfer between a Rydberg atom and a polar molecule can
be controlled by a DC electric field. Here we show how to exploit this control
for state-resolved, non-destructive detection and spectroscopy of the molecules
where the lineshape reflects the type of molecular transition. Using the
example of ammonia, we identify the conditions for collision-mediated
spectroscopy in terms of the required electric field strengths, relative
velocities, and molecular densities. Rydberg atom-enabled spectroscopy is
feasible with current experimental technology, providing a versatile detection
method as basic building block for applications of polar molecules in quantum
technologies and chemical reaction studies.
