Thomas, Rachel Victoria; (1999) Short pulse, high intensity laser interactions with molecules. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Direct measurements of the angular distributions of CO2 fragment ions produced in interactions with 750 nm laser pulses of 60 fs duration are presented. These distributions dramatically show the bent nature of the initially linear dissociating molecule and allow observation of the alignment of the different dissociation channels. The first measurements of 750 nm laser pulses of 60 fs with vibrationally excited CO2 are presented. In comparison with ground state CO2 enhanced kinetic energies of the carbon fragment ions, particularly C+, have been observed. These observations are consistent with unusually large bends in the molecule induced by the laser field. Perpendicular alignment of the molecule with the laser field is also implied. A comparison of the results of dissociative ionisation of CO2 by 750 nm laser pulses of 60 fs duration and by 532 nm laser pulses of 35 ps duration is made. Presented for the first time are the results of intense laser field dissociation of nitrous oxide using laser pulses of 35 ps duration and these results are compared to the dissociative ionisation using 750 nm laser pulses of 60 fs duration. Original results of MEDI of sulphur hexafluoride using 60 fs laser pulses at 750 nm are presented. The fragmentation pattem of SF6 displays features similar to those found in experiments with diatomic and triatomic molecules, with a tendency towards symmetric dissociative channels and producing fragment energies which for all channels are consistent with a Coulomb explosion at a single, critical, internuclear separation.

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