C60q+ (q=1, 2, 3, 4) formation by intense femtosecond laser irradiation

C60 vapor was irradiated with an intense femtosecond laser pulse (1.0×1016 W/cm2 in 100 fs at a wavelength of 790 nm). Multiply charged ions, assignable up to C604+, were observed in the time-of-flight spectra, while C60q+ (q≤2) with many fragments were detected by a nanosecond laser pulse (1.2×1013 W/cm2 in 9 ns at 532 nm). The formation of the multiply charged ions will be explained in terms of barrier suppression ionization (BSI) for the case of femtosecond excitation.