Abstract:

The resonant two-photon ionization (R2PI) spectrum of 1-naphthol (1NP) was studied from 305 to 322 nm using supersonic molecular beam technique. 1NP has two rotamers: cis and trans. The R2PI spectrum was used to characterize the S1←S0 transition of the trans species and its original band appeared at 317.8 nm (31456 cm-1). The vibrational bands of the trans species from the R2PI spectrum can be assigned to in-plane vibrational modes with a' symmetry. Ab initio and density functional theory (DFT) calculations indicate that the cis rotamer has higher energy than the trans rotamer by 439 cm-1 in the ground state but it has a lower exciting energy than the trans rotamer by 1216 cm-1 for the S1←S0 transition. These calculated results are in good agreement with the experimental trend where the difference between the cis and trans energies in the S0 state is 220 cm-1 and the difference between the cis and trans exciting energies is 274 cm-1. There are no spectral features from the cis rotamer in the R2PI spectrum and we attribute this to the efficient cooling conditions in the molecular beam, which leads to a very small cis rotamer population with the higher energy (220 cm-1).

Key words: Electronic excited state, 1-Naphthol, Resonant two-photon ionization, Ab initio calculation