Dissociative ionization of molecules by intense laser fields at 532 nm and 10¹²-10¹⁴ W cm^-2

Abstract

Ionization and dissociative ionization of N₂, CO, CS₂, CO₂ and NO₂ by intense 532 nm radiation has been studied by measuring mass spectra at incident laser intensities over the range 4.1*10¹²-1.27*10¹⁴ W cm^-2, covering a region which is intermediate between the multiphoton and tunnelling regimes. For molecules with large zero-field dissociation energies (N₂, CO) the mass spectra show the dominance of the molecular ion peak, with relatively small yields of fragment ions. For molecular species which are more loosely bound (CS₂, CO₂ and NO₂), fragment ions dominate the mass spectra. The results appear to indicate that, at 532 nm, molecules with a low zero-field dissociation energy (less than approximately 6 eV) tend to dissociate first, followed by ionization of the fragments. In the case of molecules with high zero-field dissociation energies, molecular ionization occurs first, followed subsequently by fragmentation.