The various rotamer conformations associated with the hindered ethyl group rotor in ethyl-substituted cyclohexanones and cyclopentanones have been trapped in a supersonic expansion and spectroscopically analyzed by 2 + 1 resonance-enhanced multiphoton ionization via the 3s <-- n Rydberg transition. The rapid cooling in the supersonic expansion effectively freezes many of the conformations at their room temperature equilibrium concentrations. The various rotamers, including some in the axial orientation, were identified by comparing peak intensities with those calculated by both molecular mechanics and ab initio MO methods. Excellent agreement between the calculations and the experimental results is noted.