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Title: Resolving strong field dynamics in cation states of CO2 via optimised molecular alignment
Author: Oppermann, Malte
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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In this thesis, the role of the molecular structure in strong field induced processes in CO2 is resolved by the use of optimised impulsive molecular alignment. Two processes were investigated: recollision induced ionisation and the dissociation of the molecular ion CO2+. Both processes are driven by the initial tunneling ionisation of CO2. Through the use of molecular alignment, the orbital symmetries of the involved molecular ionic states were resolved, revealing the internal molecular dynamics in the form of ionisation and excitation pathways. A novel data analysis procedure was developed to extract the alignment distribution and rotational temperature of the impulsively aligned molecular ensemble. This facilitated the optimisation of molecular alignment in mixed gas samples and was demonstrated for N2, O2 and CO2 seeded in Ar. The recollision induced or nonsequential double ionisation (NSDI) of CO2 was then studied in the molecular frame. The process was fully characterised by measuring the shape of the recolliding electron wavepacket and the angularly resolved inelastic electron-ion recollision cross section. The results reveal the contribution from both the ionic ground and first excited state of CO2+ to the NSDI mechanism. This study was extended to the strong field induced dissociation of impulsively aligned CO2+. It was found that dissociation is driven by a parallel dipole transition from the second excited ionic state B to the predissociating state C, whilst recollision excitation was shown to not play a role. The strong field induced coupling of the ionic states B and C could thus be controlled by the laser polarisation. The results obtained in this thesis further the understanding of population dynamics of cation states in strong field processes. This is of special interest for extending molecular strong field physics to the study of electronic degrees of freedom and their coupling to the nuclear motion.
Supervisor: Marangos, Jon Sponsor: European Commission
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available