Multiply ionization of benzene clusters by a nanosecond laser: Distributions of the ion charge state and the electron energy

The electron energies were measured to investigate the influences of laser intensity and wavelength on the ion charge state distribution of Cq+ (q = 2–4) when benzene clusters were irradiated by 109–1011 W/cm2 nanosecond laser pulses. The results show that the ratios of Cq+/C(q−1)+ strongly depend on laser wavelength but slightly on laser intensity. The mean electron energy up to 100 eV was measured, which was qualitatively consisted with the ‘multiphoton ionization ignition-inverse bremsstrahlung heating-electron impact ionization’ three-stage model. The screening effects inside clusters can significantly decrease the ionization potentials of Cq+ and facilitate the formation of multiply charged ions especially at low laser intensity.