Cluster-assisted multiple-ionization of methyl iodide by a nanosecond laser: Wavelength dependence of multiple-charge ions

Abstract

As efforts continue to elucidate laser–cluster interactions, we investigated the influence of laser wavelength on ion products. In this study, a pulsed methyl iodide cluster was irradiated with a Nd–YAG nanosecond laser, and the ion products were analyzed using time-of-flight mass spectrometry. Multiple-charge atomic ions of C q+ and I q+ ( q ⩾ 2) were observed using 532 and 1064 nm laser wavelengths; however, only single-charge atomic and molecular ions appeared at 266 and 355 nm. We show that the charge-state distribution for multiple-charge ions is almost independent of laser intensity. A three-stage model was developed to further understand these experimental results: the inverse electron bremsstrahlung heating rate is proportional to the square of laser wavelength, which seems to explain the dependence of multiple-charge ions on the wavelength.