Acta Phys. -Chim. Sin. ›› 2014, Vol. 30 ›› Issue (8): 1416-1425.doi: 10.3866/PKU.WHXB201405232


Rotamers of m-Methylanisole Studied by Mass-Analyzed Threshold Ionization Spectroscopy

QIN Chen1,2,3, TZENG Sheng-Yuan1, ZHANG Bing2, TZENG Wen-Bih1   

  1. 1. Laboratory for Mass Spectrometric and Spectroscopic Studies of Biomolecules, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617;
    2. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071;
    3. Key Laboratory of Novel Luminescent Materials and Nanostructures, College of Physics and Electronic Engineering, Xinjiang Normal University, Urumqi 830054
  • Received:2014-04-23 Revised:2014-05-22 Published:2014-07-18
  • Contact: TZENG Wen-Bih


The S1S0 electronic transition and threshold ionization of the cis and trans rotamers of m-methylanisole were investigated by using one- color resonant two- photon ionization and mass- analyzed threshold ionization techniques. The first electronic excitation energies (E1) of the cis and trans rotamers were determined to be (36049±2) and (36117±2) cm-1, while the adiabatic ionization energies (Ip) were (64859 ± 5) and (65110 ± 5) cm-1, respectively. The results of ab initio and density functional theory calculations provide a satisfactory interpretation for our experimental findings concerning the difference in the transitional energies of the cis and trans rotamers and assist in assigning the vibronic and cation spectra obtained in the present study. The observed active vibrations of both rotamers in the S1 and D0 states primarily consist of methyl torsion, in- plane ring deformation, and substituent- sensitive bending modes. Both experimental and theoretical results show that, for both cis and trans isomers, the geometry of the cation in the D0 state is somewhat different from that of the neutral species in the S1 state. In addition, the strengths of both the through- space substituent- substituent and substituent- ring interactions were found to follow the order: S0<S1<D0.

Key words: m-Methylanisole, Rotamer, Vibronic spectrum, Threshold ionization, Cation spectrum