First principles molecular dynamics and control of photochemical reactions
Abstract/Contents
- Abstract
- In this thesis, we develop and use an ab initio molecular dynamics method to investigate the mechanisms of photochemical reactions, working towards the goal of controlling these reactions. We use and extend the ab initio multiple spawning (AIMS) method for this purpose. AIMS solves the Schrodinger equation for both the nuclear and electronic wavefunctions on multiple potential energy surfaces (PESs) and adaptively expands the nuclear basis set at critical regions on the PES to account for nonadiabatic events. In this thesis, we improve the accuracy of the electronic wavefunction by implementing a higher level quantum chemical method, multi-state second-order perturbation theory (MS-CASPT2). AIMS with MS-CASPT2 is then applied to the photochemistry of ethylene, the prototype of photoisomerization reactions. Good agreement in terms of the excited state lifetime is achieved between theory and time-resolved experiments. The agreement demonstrates the importance of faithful comparison between experiment and simulation, and provides us with mechanistic insights for photoisomerization reactions, which lies at the center of many important phenomena in nature. AIMS is then applied to two molecules where the excited state dynamics may be controlled in different ways. In the case of propanal cation, we show that careful initial state preparation can lead to distinct excited state dynamics and the effects of this distinct dynamics persist in the product distribution which is formed through dissociation on the ground electronic state. AIMS reveals the mechanism of the dramatic branching ratio difference between two product channels measured by experimentalists, and identifies the critical role of conical intersections and dark states in causing the observed conformational selectivity. We follow our study of the excited dynamics with modeling of the ground state kinetics, which allows us to make a quantitative comparison with experiment. We then investigate the potential for control of the ring-opening reaction of cyclohexadiene (CHD), using an external laser field to alter the dynamics after photoexcitation. We explicitly incorporate light-matter interactions within the framework of AIMS. The augmented method is first tested on one- and two-dimensional model problems before applying it to the CHD ring-opening reaction. The results of the extended AIMS method are compared to recent experiments on CHD and we are able to successfully predict the change in product branching ratio as a function of the time delay between the excitation and control pulses. In conclusion, our recent improvements in the accuracy of the underlying electronic structure and the incorporation of an explicit treatment of light-matter interactions have made AIMS more powerful as a means of understanding photochemical reactions and designing control strategies.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2011 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Tao, Hongli |
|---|---|
| Associated with | Stanford University, Department of Chemistry |
| Primary advisor | Martinez, Todd J. (Todd Joseph), 1968- |
| Thesis advisor | Martinez, Todd J. (Todd Joseph), 1968- |
| Thesis advisor | Andersen, Hans, 1941- |
| Thesis advisor | Bucksbaum, Philip H |
| Advisor | Andersen, Hans, 1941- |
| Advisor | Bucksbaum, Philip H |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Hongli Tao. |
|---|---|
| Note | Submitted to the Department of Chemistry. |
| Thesis | Ph.D. Stanford University 2011 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2011 by Hongli Tao
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...