2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/157832We have selected and spatially separated the two conformers of 3-aminophenol (C$_6$H$_7$NO) present in a molecular beam. Analogous to the separation of ions based on their mass-to-charge ratios in a quadrupole mass filter, the neutral conformers are separated based on their different mass-to-dipole-moment ratios in an ac electric quadrupole selector. For a given ac frequency, the individual conformers experience different focusing forces, resulting in different transmissions through the selector. These experiments demonstrate that conformer-selected samples of large molecules can be prepared, offering new possibilities for the study of gas-phase biomolecules.4 pages, 4 figures (Revtex)Chemical PhysicsAtomic and Molecular ClustersBiological Physicstext