Cluster ion formation from a liquid surface of solutions of naphthalene. Photosensitization effect of naphthalene

An ethanol solution of naphthalene was introduced into vacuum as a continuous liquid flow (liquid beam) and was irradiated with a laser beam at the wavelength of 275 nm. Ions produced by multiphoton ionization in the liquid beam and ejected from it were analyzed by a reflectron time-of-flight mass spectrometer. The dominant ions produced were protonated ethanol cluster ions, H⁺(EtOH)_n. In addition, naphthalene-ethanol cluster ions, Np⁺(EtOH)_n, and a naphthalene dimer ion, Np₂⁺, were observed. The ion species, Np⁺(EtOH)_n and Np₂⁺, are considered to be produced by multiphoton ionization of naphthalene followed by ejection from the liquid surface. In order to confirm the assignments of the ions from the liquid beam of the ethanol solution, the ions ejected from methanol and 1-propanol solutions of naphthalene were also observed. On the other hand, the formation of H⁺(EtOH)_n, are explained in terms of proton transfer from a naphthalene ion to ethanol molecules, where naphthalene acts as a photosensitizer for the formation of H⁺(EtOH)_n.