REMPI and MATI spectroscopy of cis and trans 3-chloro-N-methylaniline

The Resonance-enhanced two-photon ionization (R2PI) and Mass-analyzed threshold ionization (MATI) spectra of 3-Chloro-N-methylaniline (3CINMA) were recorded in detail. The experimental and calculated results revealed that cis and trans 3CINMA are the only two stable conformers for each of the S-0, S-1 and D-0 states. The first electronic excitation energies (E(1)s) of cis and trans Cl-35-3CINMA were measured to be 33,003 +/- 3 and 32,886 +/- 3 cm(-1) by R2PI spectroscopy. The adiabatic ionization energies (IEs) of cis and trans 35C1-3CINMA were determined to be 61,531 +/- 5 and 61,625 +/- 5 cm(-1) by MATI spectroscopy. The E1s and IEs of cis and trans Cl-37-3CINMA were also obtained and found to be identical to that of the Cl-35-3CINMA rotamers. Compared with the trans rotamer, the cis rotamer is less stable by 50 cm(-1) in the Si state, but more stable by 67 and 161 cm(-1) in So and Do states. Most of the active vibration modes observed in the R2PI and MATI spectra are in-plane ring deformation and substituent-sensitive modes. Detailed analysis reveals a correlation between the typical ring vibration frequencies and the relative stability of the two rotamers, suggesting that the conformation effect on the ring rigidity plays a key role in determining the relative stability of the conformers. The ab initio and density functional theory (DFT) calculations were performed to analyze the substitution and conformation effects on the properties of 3CINMA rotamers. (C) 2017 Elsevier Inc. All rights reserved