Generation of multi-charged ions in laser-induced ionization of methanol under intense nanosecond laser fields

The photoionization of methanol seeded in He, N2, Ar gases by an inten se 25ns NdYAG 532nm laser has been studied by timeofflight mass spectrome try . At the laser intensity about 1011W·cm-2, strong multicharged io ns Cq+(q=2—4) and Oq+(q=2—4) appeared in the mass spectra apart from the ions coming from multiphoton ionization (MPI) process when Ar w as used as a carrier gas. From the simulation, we can find the vel ocity of multicharged ions is distributed in Gaussian shape with a FWHM of 6 4×104 m/s. From the experimental results of changing carrier gases and changi ng the delay time of the pulsed electric field, the conclusion can be drawn that th ose multicharged ions come from the Coulomb explosion of methanol cluster ions .