  We report on the collisional shift and line broadening of Rydberg states in
nitric oxide (NO) with increasing density of a background gas at room
temperature. As a background gas we either use NO itself or nitrogen (N$_{2}$).
The precision spectroscopy is performed by a sub-Doppler three-photon
excitation scheme with a subsequent readout of the Rydberg states realized by
the amplification of a current generated by free charges due to collisions. The
shift shows a dependence on the rotational quantum state of the ionic core and
no dependence on the principle quantum number of the orbiting Rydberg electron.
The experiment was performed in the context of developing a trace-gas sensor
for breath-gas analysis in a medical application.
