The photoionization of seeded carbon bisulfide molecular beam by a 1064nm nanosecond Nd-YAG laser with intensities varying from 0.8 × 10^11 to 5.6 × 10^11 W/cm^2 have been studied by time-of-flight mass spectrometry. Multiply charged ions of S^q＋ （q = 2 6） and C^q＋ （q = 2-4） with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS2 neat clusters in the beam. An electron reeolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.
The multi-charged sulfur ions of Sq^＋ （q ≤ 6） have been generated when hydrogen sulfide cluster beams are irradiated by a nanosecond laser of 1064 and 532 nm with an intensity of 10^10- 10^12W.cm^-2. S^6＋ is the dominant multicharged species at 1064 nm, while S^4＋, S^3＋ and S^2＋ ions are the main multi-charged species at 532 nm. A three-step model （i.e., multiphoton ionization triggering, inverse bremsstrahlung heating, electron collision ionizing） is proposed to explain the generation of these multi-charged ions at the laser intensity stated above. The high ionization level of the clusters and the increasing charge state of the ion products with increasing laser wavelength are supposed mainly due to the rate-limiting step, i.e., electron heating by absorption energy from the laser field via inverse bremsstrahlung, which is proportional to λ2,λA being the laser wavelength.
