One-colour resonant two-photon ionization spectrum of the 1-fluoronaphthalene dimer and ab initio calculation

The one-colour resonant two-photon ionization (R2PI) spectrum of the 1-fluoronaphthalene (IFN) dimer has been studied in the wavelength range of 304 to 322 nm by using a supersonic molecular beam and time-of-flight mass spectrometry. Compared with the original band 0(0)(0) (at 313.8 nm) of the S-1 <- S-0 transition of the IFN monomer, a red-shifted band was observed in the IFN dimer spectrum at about 315 nm with a relatively large linewidth, nearly 2 nm. Based on the consideration of inductive effect and ab initio calculations, this red-shifted band is assigned to the first electronic excited transition of the IFN dimer. A possible geometric structure of the IFN dimer is also obtained with calculations that the two IFN molecules are combined through two hydrogen bonds which are formed between the hydrogen atom of a molecule and the fluorine atom of a neighbouring molecule. A time-dependent calculation was also carried out and the results are consistent with the experimental data.