Combination of the molecular beam, two-color resonant two-photon ionization, and mass-analyzed threshold ionization spectroscopic techniques can be used to record the vibrationally resolved spectra of rotational isomers (rotamers) in the electronically excited S₁ and cationic ground D₀ states. These vibronic and cation spectra can be used as the fingerprints for identification of the selected rotamers. Analysis of these experimental data leads us to have better insights into substitution and conformational effects on various molecular properties.