The first electronic excitation and adiabatic ionization energies of Cl-35 and Cl-37 4-chlorostyrene were similar, with values of 33,977 +/- 2 and 67,972 +/- 5 cm(-1), respectively. The general features in the obtained vibronic and cation spectra of the two isotopologues were similar. A frequency shift of 1-5 cm(-1) was observed on many active vibrations of the Cl-35 and Cl-37 isotopologues of 4-chlorostyrene in the S-1 and D-0 states. This frequency difference at each mode may reflect the degree of Cl atom involvement in the overall vibration. (C) 2017 Elsevier B.V. All rights reserved.