ZEKE spectra of propylaniline were recorded by exciting 13 vibronic levels in the S1 electronic state. All ZEKE spectra show well resolved vibrational structure of the anti and gauche cations. Adiabatic ionization potentials of the anti and gauche conformations were determined to be 59 717+/-3 cm-1 (7.4040 eV) and 59 793+/-3 cm-1 (7.4134 eV), respectively. A number of ring modes as well as several low-frequency torsional and bending chain modes have been identified. Spectra demonstrate that low-frequency chain modes are sensitive to the molecular conformation. Ab initio calculations were performed to understand the nature of these low-frequency chain modes. S1<--S0 vibronic transitions involving anti and gauche conformations can easily be distinguished using the ZEKE method.