REMPI and MATI spectroscopic study of selected cis and trans 3-chlorostyrene rotamers

Abstract The ab initio and DFT calculations predict two stable rotamers, cis and trans , for 3-chlorostyrene in each of the S 0 , S 1 and D 0 states. In the two-color resonant two-photon ionization (2C-R2PI) spectra, the band origins of S 1  ← S 0 electronic transition of cis and trans 3-chlorostyrene appears respectively at 33 766 ± 3 and 34 061 ± 3 cm −1 . The mass-analyzed threshold ionization (MATI) spectra give the adiabatic ionization energies of 69 701 ± 4 cm −1 and 69 571 ± 4 cm −1 for cis and trans rotamers. Within the experimental detection limit, the measured transition energies are the same for both the 35 Cl and 37 Cl isotopomers. The observed active modes of rotamers in the S 1 and D 0 states involve mainly the in-plane ring deformation and substituent-sensitive bending vibration. It is derived from the 2C-R2PI and MATI spectroscopic data that the cis rotamer is more stable than the trans rotamer by 218 ± 30, 513 ± 30 and 88 ± 30 cm −1 for the S 0 , S 1 and D 0 states, respectively.