Resonance enhanced multiphoton ionization spectroscopy and theoretical calculations of cis and trans p-methoxystyrene rotamers

The structures and vibrations of p-methoxystyrene in the first electronically excited state (S1) were studied by mass analyzed resonance-enhanced two photon ionization (R2PI) spectroscopy and theoretical calculations. The ab initio and the density functional theory (DFT) calculations reveal that two rotamers, cis and trans, are stable in both the ground S0 state and the excited S1 state, and their optimized molecular geometries are achieved. The band origins of the S1 ← S0 electronic transition of cis and trans p-methoxystyrene are measured to be 33242 and 33324 cm−1, respectively. Assignment of the observed spectral bands of the two rotamers in the excited S1 state was made mainly based on the ab initio calculations and the conformity with the available data in the literature.