Intensity-selective, field-induced dissociative ionization of CS₂ by femtosecond-duration light pulses

Abstract

Intensity-selective time-of-flight (TOF) spectrometry has been applied to probe the morphology of the dissociative ionization (DI) pattern obtained when linear triatomic, carbon disulfide, is irradiated by 100 fs long laser pulses over a range of intensities (10¹³-10¹⁵ W cm^-2). The measured DI pattern is very different to that obtained when measurements are made in the spatially averaged (intensity-averaged) mode conventionally used in TOF spectrometry. Our results indicate that single ionization of the parent molecule occurs predominantly in the wings of the focus; the most intense parts of the focal region have a preponderance of highly charged atomic fragments as compared to the wings. Correlation is established between the kinetic energy release (KER) accompanying dissociation of multiply charged molecular ions and the spatial region at which such ion production has occurred. Anisotropic angular distributions of S⁺ and S²⁺ fragment ions are used to deduce that CS₂ is geometrically aligned along the direction of the laser polarization vector due to the dependence of the ionization rate on the polarization angle. Evidence was sought, but not found, for dynamic alignment due to reorientation of the S-C-S axis along the laser polarization vector.