Computationally exploring ultrafast molecular ionization
dc.contributor.author | Yu, Youliang | |
dc.date.accessioned | 2017-12-15T17:02:16Z | |
dc.date.available | 2017-12-15T17:02:16Z | |
dc.date.graduationmonth | May | en_US |
dc.date.issued | 2018-05-01 | en_US |
dc.date.published | 2018 | en_US |
dc.description.abstract | Strong-field ionization plays a central role in molecules interacting with an intense laser field since it is an essential step in high-order harmonic generation thus in attosecond pulse generation and serving as a probe for molecular dynamics through either the sensitivity of ionization to the internuclear separation or the laser-induced electron scattering. Strong-field molecular ionization has been studied both theoretically and experimentally, dominantly through the Born-Oppenheimer approximation and at equilibrium or small reaction distances. We have extended the theoretical studies of molecular ionization to a much broader extent. Specifically, due to the difficulty of treating ionization in Born-Oppenheimer representation especially for molecular dynamics involving strongly-correlated electron-nuclear motion, we have investigated an alternative time-independent--adiabatic hyperspherical--picture for a one-dimensional model of the hydrogen molecule. In the adiabatic hyperspherical representation, all the reaction channels--including ionization--for the hydrogen molecule have been identified in a single set of potential curves, showing the advantage of studying molecular dynamics involving multiple breakup channels coupled with each other. We have thus proposed a good candidate to study strongly-correlated molecular dynamics, such as autoionization and dissociative recombination. Moving to a time-dependent picture by numerically solving the time-dependent Schrödinger equation (TDSE), we have explored two extreme classes of strong-field ionization of hydrogen molecule ion: at large internuclear distances (R>30 a.u.) and for long-wavelength laser fields. Remarkably, we have found strong-field two-center effects in molecular ionization beyond the long-standing one-photon two-center interference as a manifestation of the double-slit interference. In particular, the total ionization probability at large internuclear distances shows strongly symmetry-dependent two-center dynamics in homonuclear diatomic molecules and two-center induced carrier-envelope phase effect in heteronuclear diatomic molecules. Such two-center effects are expected to generalize to other diatomic systems and could potentially be used to explain phenomena in multi-center strong-field physics. Moreover, we have theoretically confirmed, for the first time, the existence of low energy structure in molecular ionization in long-wavelength laser fields by solving the three-dimensional TDSE. Finally, we have performed a pump-probe study of the hydrogen molecular ion where a pump pulse first dissociates the molecule followed by a probe pulse which ionizes the dissociating wave packet, and surprisingly found a pronounced broad ionization peak at large R or large pump-probe delay (~150 fs). Numerically, we have developed and implemented new theoretical frameworks to more accurately and efficiently calculate quantum mechanical processes for small molecules--hydrogen molecule and its ion--which could readily be adapted to heavier diatomic systems. | en_US |
dc.description.advisor | Brett D. Esry | en_US |
dc.description.degree | Doctor of Philosophy | en_US |
dc.description.department | Department of Physics | en_US |
dc.description.level | Doctoral | en_US |
dc.description.sponsorship | Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy under Award DE-FG02-86ER13491 | en_US |
dc.identifier.uri | http://hdl.handle.net/2097/38548 | |
dc.language.iso | en | en_US |
dc.publisher | Kansas State University | en |
dc.subject | Physics | en_US |
dc.subject | Ultrafast | |
dc.subject | Strong-field | |
dc.subject | Molecular dynamics | |
dc.title | Computationally exploring ultrafast molecular ionization | en_US |
dc.type | Dissertation | en_US |