Doctor of Philosophy / Department of Physics / Itzhak Ben-Itzhak / Lasers are being used widely for the study and manipulation of the dynamics of atomic
and molecular targets, and advances in laser technology makes it possible to explore new
areas of research — for example attosecond physics. In order to probe the fragmentation
dynamics of molecular ions, we have developed a coincidence three-dimensional momentum
imaging method that allows the kinematically complete study of all fragments except
electrons. Recent upgrades to this method allow the measurement of slow dissociation fragments,
down to nearly zero velocity, in intense ultrafast laser fields. Evidences for the low
energy breakup are presented using the benchmark molecules diatomic H[subscript]2[superscript]+ and polyatomic
H[subscript]3[superscript]+ . The low energy fragments in H[subscript]2[superscript]+ dissociation are due to the intriguing zero-photon dissociation
phenomenon. This first experimental evidence for the zero-photon dissociation is
further supported by sophisticated theoretical treatment. We have explored the laser pulse
length, intensity, wavelength, and chirp dependence of zero-photon dissociation of H[subscript]2[superscript]+, and
the results are well described by a two-photon process based on stimulated Raman scattering.
Similar studies of the slow dissociation of H[subscript]3[superscript]+ reveal that two-body dissociation is dominant
over three-body dissociation. The most likely pathways leading to low-energy breakup into
H[superscript]++H[subscript]2, in contradiction to the assessments of the channels in at least one previous study,
are explored by varying the laser pulse duration and the wavelength. In addition, we have
investigated the dissociation and single ionization of N[subscript]2[superscript]+ , and an interesting high energy feature
in addition to the low energy has been observed at higher intensities. Such high energy
results from the breakup of molecules in excited states are accessible at higher intensities
where their potential energy is changing rapidly with the internuclear distance. We have
extended the intense field ionization studies to other molecular ions N[subscript]2[superscript]+ , CO[superscript]+, NO[superscript]+, and
O[subscript]2[superscript]+ . The dissociative ionization of these molecules follow a general mechanism, a stairstep
ionization mechanism. Utilizing the capability of the upgraded experimental method we
have measured the non-dissociative and dissociative ionization of CO[superscript]+ using different pulse
lengths. The results suggest that dissociative ionization can be manipulated by suppressing
some ionization paths.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/8852 |
| Date | January 1900 |
| Creators | Gaire, Bishwanath |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
Page generated in 0.0021 seconds