Conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color REMPI (resonance enhanced multiphoton ionization) and MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Gauche- and anti-cationic conformers were selectively produced by two-color excitation via the respective S-1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70148 and 69955+/-5 cm(-1), respectively. Analysis of the REMPI and MATI spectra allowed the determination of the S-0 (38 cm(-1)), S-1 (100 cm(-1)), and D-0 (-155 cm(-1)) gauche- and anti-conformer energy differences. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations discussed. (C) 2003 American Institute of Physics.