Photoionization Spectroscopic and Theoretical Study on the Molecular Structures of cis- and trans-3-Chlorothioanisole

[Image: see text] Resonance-enhanced two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) spectra are measured for the cis- and trans-3-chlorothioanisole (3ClTA). The first electronic excitation energy (E(1)) and the adiabatic ionization energy (IE) of the cis-rotamer are determined to be 33 959±3 and 65 326±5 cm(–1), respectively, and those of the trans-rotamer are determined to be 34102±3 and 65 471±5 cm(–1), respectively. Density functional theory (DFT) calculations confirm that both the cis- and trans-rotamers of 3ClTA are stable and coexist in their respective S(0), S(1), and D(0) states. Both rotamers adopt planar structures with cis- being slightly more stable than trans- in the respective S(0), S(1), and D(0) states. The conformation, substitution, and isotope effects on the molecular structure, active vibrations, and electronic transition and ionization energies of 3ClTA are analyzed.