Doctor of Philosophy / Department of Physics / Brett D. Esry / The nuclear rotational period of the simplest molecule H[subscript]2[superscript]+ is about 550 fs, which is more
than 35 times longer than its vibrational period of 15 fs. The rotational time scale is also
much longer than widely available ultra short laser pulses which have 10 fs or less duration.
The large difference in rotational period and ultra short laser pulse duration raises questions
about the importance of nuclear rotation in theoretical studies of H[subscript]2[superscript]+ dissociation by these
pulses. In most studies, reduced-dimensionality calculations are performed by freezing the
molecular axis in one direction, referred to as the aligned model. We have systematically
compared the aligned model with our full-dimensionality results for total dissociation probability
and field-free dynamics of the dissociating fragments. The agreement between the
two is only qualitative even for ultra short 10 fs pulses. Post-pulse dynamics of the bound
wave function show rotational revivals. Significant alignment of H[subscript]2[superscript]+ occurs at these revivals.
Our theoretical formulation to solve the time-dependent Schrodinger equation is an important
step forward to make quantitative comparison between theory and experiment. We
accurately calculate observables such as kinetic energy, angular, and momentum distributions.
Reduced-dimensionality calculations cannot predict momentum distributions. Our
theoretical approach presents the first momentum distribution of H[subscript]2[superscript]+ dissociation by few cycle
laser pulses. These observables can be directly compared to the experiment. After
taking into account averaging steps over the experimental conditions, we find remarkable
agreement between the theory and experiment. Thus, our theoretical formulation can make
predictions. In H[subscript]2[superscript]+ dissociation by pulses less than 10 fs, an asymmetry in the momentum
distribution occurs by the interference of different pathways contributing to the same energy.
The asymmetry, however, becomes negligible after averaging over experimental conditions.
In a proposed pump-probe scheme, we predict an order of magnitude enhancement in the
asymmetry and are optimistic that it can be observed.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/2181 |
| Date | January 1900 |
| Creators | Anis, Fatima |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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