DISSOCIATIVE IONIZATION OF MOLECULES BY INTENSE LASER FIELDS AT 532 NM AND 10(12)-10(14) CM(-2)

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 x 10(12)-1.27 x 10(14) W cm-2, covering a region which is intermediate between the multiphoto n and tunnelling regimes. For molecules with large zero-field dissocia tion energies (N2, CO) the mass spectra show the dominance of the mole cular ion peak, with relatively small yields of fragment ions. For mol ecular species which are more loosely bound (CS2, CO2 and NO2), fragme nt ions dominate the mass spectra. Our 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 ioniza tion of the fragments. In the case of molecules with high zero-field d issociation energies, molecular ionization occurs first, followed subs equently by fragmentation.