[en] Highlights: • The vibronic and cation spectra of 4-chlorostyrene are recorded. • The electronic excitation and ionization energies are precisely determined. • The spectra show a frequency shift for the isotopologues of 4-chlorostyrene. The first electronic excitation and adiabatic ionization energies of ³⁵Cl and ³⁷Cl 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 ³⁵Cl and ³⁷Cl isotopologues of 4-chlorostyrene in the S₁ and D₀ states. This frequency difference at each mode may reflect the degree of Cl atom involvement in the overall vibration.