We applied the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques to investigate the ionic properties of the selected rotamers of p-methoxystyrene. The adiabatic ionization energies of cis- and trans-p-methoxystyrene are determined to be 62 487 +/- 5 and 62 512 +/- 5 cm (1), respectively. Most of the observed active vibrations involve in-plane ring and substituent-sensitive motions. Our experimental results show that different orientation of the methoxyl group with respect to the vinyl group only slightly influence these cation vibrations, depending on the degree of involvement of the substituents involved in the overall vibrations. (C) 2011 Elsevier B. V. All rights reserved.