Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

- We report the vibronic and cation spectra of cis- and trans-m-chloroanisole.
- Spectral features mainly result from substituent-sensitive and in-plane ring vibrations.
- The chlorine substituent can influence the transition energy and molecular vibration.

We apply the resonant two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) techniques to record the vibronic and cation spectra of m-chloroanisole. The vibronic features appear in two series, built on 35,822 ± 2 and 35,868 ± 2 cm−1, corresponding to the origins of the S1 ← S0 electronic transition (E1's) of the two rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 67,645 ± 5 and 68,008 ± 5 cm−1 for these two isomeric species. Comparing these data with those of anisole, we find that the chlorine substitution at the meta position leads to a red shift in the E1 and a blue shift in the IE. The observed R2PI and MATI bands mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations of these species in the electronically excited S1 and cationic ground D0 states.