Photoelectron Imaging and Photofragmentation of Molecular and Cluster Anions

Persistent Link:
http://hdl.handle.net/10150/317044
Title:
Photoelectron Imaging and Photofragmentation of Molecular and Cluster Anions
Author:
Khuseynov, Dmitry
Issue Date:
2014
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The electronic structure and photofragmentation dynamics of several molecular and cluster anions have been investigated in the gas phase via negative ion velocity-map imaging photoelectron spectrometer combined with tandem time-of-flight (TOF) mass spectrometry. Among others, photoelectron imaging investigation of the halogen- and cyano- substituted methyl radicals and corresponding carbenes has been performed on several mono- and hetero- substituted species – dicyanomethyl and chlorocyanomethyl radicals, ·CH(CN)₂ and ·CHClCN, and corresponding carbenes, NCCCN and CClCN. The results are discussed in comparison with the corresponding dichloro- species, focusing on the divergent effects of the halogen and pseudohalogen (CN) substitutions. A cooperative (captodative) interaction of π-donor Cl and π-acceptor cyano groups favors the increased stability of the CHClCN radical, but a competition of the two substituents is observed in the singlet-triplet splitting of the carbene. The experimental results are consistent with high level ab-initio calculations using the spin-flip approach in combination with the coupled-cluster theory. The C-H bond dissociation energies were determined for several substituted methanes and discussed. Additionally, a practical model is presented for describing the energy dependence of laboratory-frame photoelectron angular distributions in direct photodetachment from (in principle) any molecular orbital using linearly polarized light. A transparent mathematical approach is used to generalize the Cooper-Zare central-potential model to initial states of any mixed character. In the limits of atomic photodetachment or photoionization, the model reproduces the Cooper-Zare formula. In the case of electron emission from an orbital described as a superposition of s- and p-type functions, the model yields the previously obtained s-p mixing formula. The formalism is further advanced using the Hanstorp approximation, valid for anion photodetachment only, whereas the relative scaling of the partial wave cross-sections is assumed to follow the Wigner threshold law. The resulting model can be used to describe the energy dependence of photoelectron anisotropy for any atomic, molecular, or cluster anions. As a benchmark case, we compare the predictions of the p-d variant of the model to the experimental results for NO⁻ photodetachment and show that the observed anisotropy trend is described well using physically meaningful values of the model parameters.
Type:
text; Electronic Dissertation
Keywords:
carbenes; photoelectron imaging; photofragmentation; radicals; spectroscopy; Chemistry; angular distribution
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Sanov, Andrei

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titlePhotoelectron Imaging and Photofragmentation of Molecular and Cluster Anionsen_US
dc.creatorKhuseynov, Dmitryen_US
dc.contributor.authorKhuseynov, Dmitryen_US
dc.date.issued2014-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe electronic structure and photofragmentation dynamics of several molecular and cluster anions have been investigated in the gas phase via negative ion velocity-map imaging photoelectron spectrometer combined with tandem time-of-flight (TOF) mass spectrometry. Among others, photoelectron imaging investigation of the halogen- and cyano- substituted methyl radicals and corresponding carbenes has been performed on several mono- and hetero- substituted species – dicyanomethyl and chlorocyanomethyl radicals, ·CH(CN)₂ and ·CHClCN, and corresponding carbenes, NCCCN and CClCN. The results are discussed in comparison with the corresponding dichloro- species, focusing on the divergent effects of the halogen and pseudohalogen (CN) substitutions. A cooperative (captodative) interaction of π-donor Cl and π-acceptor cyano groups favors the increased stability of the CHClCN radical, but a competition of the two substituents is observed in the singlet-triplet splitting of the carbene. The experimental results are consistent with high level ab-initio calculations using the spin-flip approach in combination with the coupled-cluster theory. The C-H bond dissociation energies were determined for several substituted methanes and discussed. Additionally, a practical model is presented for describing the energy dependence of laboratory-frame photoelectron angular distributions in direct photodetachment from (in principle) any molecular orbital using linearly polarized light. A transparent mathematical approach is used to generalize the Cooper-Zare central-potential model to initial states of any mixed character. In the limits of atomic photodetachment or photoionization, the model reproduces the Cooper-Zare formula. In the case of electron emission from an orbital described as a superposition of s- and p-type functions, the model yields the previously obtained s-p mixing formula. The formalism is further advanced using the Hanstorp approximation, valid for anion photodetachment only, whereas the relative scaling of the partial wave cross-sections is assumed to follow the Wigner threshold law. The resulting model can be used to describe the energy dependence of photoelectron anisotropy for any atomic, molecular, or cluster anions. As a benchmark case, we compare the predictions of the p-d variant of the model to the experimental results for NO⁻ photodetachment and show that the observed anisotropy trend is described well using physically meaningful values of the model parameters.en_US
dc.typetexten
dc.typeElectronic Dissertationen
dc.subjectcarbenesen_US
dc.subjectphotoelectron imagingen_US
dc.subjectphotofragmentationen_US
dc.subjectradicalsen_US
dc.subjectspectroscopyen_US
dc.subjectChemistryen_US
dc.subjectangular distributionen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorSanov, Andreien_US
dc.contributor.committeememberSanov, Andreien_US
dc.contributor.committeememberMonti, Oliveren_US
dc.contributor.committeememberSchwartz, Stevenen_US
dc.contributor.committeememberLichtenberger, Dennisen_US
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