Vibrational spectrum and ab initio calculations of m-xylene

We present an assigned spectrum of the first electronic transition of m-xylene observed by resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. The band origin of the S1 ← S0 electronic transition is found to be 36 951 cm−1. These vibrationally resolved spectral features have been successfully assigned on the basis of comparison with the results from ab initio and density functional theory calculations. These suggest that the substituents on benzene ring can influence the electronic transition and molecular vibrational modes of m-xylene. The spectrum shows a rich structure and some vibrational frequencies of S1 state are determined.