Non-adiabatic photodissociation dynamics of BrCl and BrNO
| dc.contributor.author | Loock, Hans-Peter | |
| dc.contributor.supervisor | Qian, C. X. W. | |
| dc.date.accessioned | 2018-07-18T17:49:44Z | |
| dc.date.available | 2018-07-18T17:49:44Z | |
| dc.date.copyright | 1996 | en_US |
| dc.date.issued | 2018-07-18 | |
| dc.degree.department | Department of Chemistry | |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | Photodissociation experiments on expansion cooled bromine chloride (BrCl) and nitrosyl bromide (BrNO) were conducted using a pump / probe scheme. Resonance-enhanced- multiphoton- ionization (REMPI) spectroscopy allowed for state selective ionization of the photofragments. Using time-of-flight mass spectrometry (TOF-MS), it was possible to make use of the E-μ-ν vector correlation in order to identify, and characterize, the parent molecule's excited electronic states. Photodissociation experiments on BrCl were carried out at six wavelengths between 500 nm and 389 nm. These experiments established the [special characters omitted]) fragment channel as one of the diabatic dissociation limits of the [special characters omitted] state. Application of the theory of diatomic dissociation as developed by Singer, Freed and Band (J. Chem. Phys., 79, (1983), 6060) led to a new diabatic correlation diagram. This correlation diagram explained not only our experimental results well, but was also coherent with earlier experimental and theoretical investigations on other interhalogens. The UV-Vis absorption spectrum of BrNO was recorded. At ten wavelengths between 740 nm and 225 nm photodissociation experiments were carried out. Guided by comparison with the well-studied CINO dissociation dynamics, we propose the BrNO frontier orbitals and assign the absorption bands to the various low lying electronic transitions. The absorption from 740 nm to 370 nm is dominated by transitions to triplet states, which borrow intensity from the higher energy singlet state, S5. A diabatic correlation diagram was constructed to aid an understanding of the photodissociation dynamics. These considerations combined with the recorded fragment quantum state distributions led to a qualitative understanding of the topology of the excited state potential energy surfaces. Non-adiabatic interactions following excitation to the [special characters omitted] state of BrNO were investigated and could be understood with our correlation diagram. We observed a strong correlation of the adiabalicity of the photodissociation process to the NO rotational levels. This indicates that the interaction region of the [special characters omitted] state with the S3 and/or S4 state is located early in the dissociation coordinate but late in the bending coordinate. The lowest lying triplet state, T1 absorbs via two vibrational adiabats which correlate to NO fragments in their v" = 0 and v" = 1 vibrational state, respectively. The NO rotational distribution is bimodal indicating that the excited state is rather shallow. Following excitation at 355 nm a narrow oscillation of the spatial distribution from a cos2θ distribution to a sin2θ distribution was observed as a function of the NO rotational excitation. Assuming that this effect is due to an interference between different excitation/dissociation pathways, two tentative explanations based on the new correlation diagram are offered. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/9713 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.subject | Photoionization | en_US |
| dc.subject | Dissociation | en_US |
| dc.title | Non-adiabatic photodissociation dynamics of BrCl and BrNO | en_US |
| dc.type | Thesis | en_US |