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SYMMETRY IN THE DISSOCIATIVE RECOMBINATION OF POLYATOMIC IONS AND IN ULTRA-COLD FEW BODY COLLISIONS

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Date Issued:
2010
Abstract/Description:
We discuss the role of symmetries in the dissociative recombinations (DR) of three polyatomic ions, namely the linear HCO+ (formyl) ion and the two highly symmetric H3+ and H3O+ (hydronium) molecular ions. Regarding the HCO+ ion, we apply a quantum mechanical treatment using the Multi-channel Quantum Defect Theory (MQDT) formalism to describe the ion-electron scattering process. Our study takes into account the Renner-Teller effect in order to model the non Born-Oppenheimer vibronic coupling in linear polyatomic ions. The coupling has shown to represent the main mechanism responsible for electronic capturing in highly excited Rydberg states associated with excited vibrational levels of the ionic core. We consider all internal degrees of freedom of HCO+ and obtain the dissociative cross section as a function of the incident electron kinetic energy. We have also improved the theoretical approach by including the large permanent dipole moment of HCO+ using a generalization of the MQDT formalism. To our knowledge, this is the first time the permanent dipole moment of an ion is included in a DR study. The obtained results are in good agreement with experimental data. W also study the DR of H3+ and H3O+ symmetric ions using a simplified theoretical treatment, which focuses on the key ingredient of the DR process, the electron capture in the first excited degenerate vibrational normal mode of the ions through non Born-Oppenheimer Jahn-Teller coupling. For both ions the obtained cross sections are in very good agreement with the available experimental data. Moreover, in the case of H3+, the results reproduce previous calculations from two independent theoretical studies. Finally, we investigate the role of symmetries in few body ultra-cold collisions by considering both three and four identical atoms systems. We derive allowed rearrangements of different fragments of the system, satisfying the complete symmetry of the molecular Hamiltonian. For that purpose we establish a correspondence between constants of motion of the system in different large-distance configurations and irreducible representations of the total symmetry group. Selection rules (forbidden transitions) and allowed states, which depend on the fermionic or bosonic nature of the atoms, can be derived from these results.
Title: SYMMETRY IN THE DISSOCIATIVE RECOMBINATION OF POLYATOMIC IONS AND IN ULTRA-COLD FEW BODY COLLISIONS.
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Name(s): Douguet, Nicolas, Author
Kokoouline, Viatcheslav, Committee Chair
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2010
Publisher: University of Central Florida
Language(s): English
Abstract/Description: We discuss the role of symmetries in the dissociative recombinations (DR) of three polyatomic ions, namely the linear HCO+ (formyl) ion and the two highly symmetric H3+ and H3O+ (hydronium) molecular ions. Regarding the HCO+ ion, we apply a quantum mechanical treatment using the Multi-channel Quantum Defect Theory (MQDT) formalism to describe the ion-electron scattering process. Our study takes into account the Renner-Teller effect in order to model the non Born-Oppenheimer vibronic coupling in linear polyatomic ions. The coupling has shown to represent the main mechanism responsible for electronic capturing in highly excited Rydberg states associated with excited vibrational levels of the ionic core. We consider all internal degrees of freedom of HCO+ and obtain the dissociative cross section as a function of the incident electron kinetic energy. We have also improved the theoretical approach by including the large permanent dipole moment of HCO+ using a generalization of the MQDT formalism. To our knowledge, this is the first time the permanent dipole moment of an ion is included in a DR study. The obtained results are in good agreement with experimental data. W also study the DR of H3+ and H3O+ symmetric ions using a simplified theoretical treatment, which focuses on the key ingredient of the DR process, the electron capture in the first excited degenerate vibrational normal mode of the ions through non Born-Oppenheimer Jahn-Teller coupling. For both ions the obtained cross sections are in very good agreement with the available experimental data. Moreover, in the case of H3+, the results reproduce previous calculations from two independent theoretical studies. Finally, we investigate the role of symmetries in few body ultra-cold collisions by considering both three and four identical atoms systems. We derive allowed rearrangements of different fragments of the system, satisfying the complete symmetry of the molecular Hamiltonian. For that purpose we establish a correspondence between constants of motion of the system in different large-distance configurations and irreducible representations of the total symmetry group. Selection rules (forbidden transitions) and allowed states, which depend on the fermionic or bosonic nature of the atoms, can be derived from these results.
Identifier: CFE0003552 (IID), ucf:48896 (fedora)
Note(s): 2010-12-01
Ph.D.
Sciences, Department of Physics
Masters
This record was generated from author submitted information.
Subject(s): Atomic
Molecular
Physics
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0003552
Restrictions on Access: campus 2013-12-01
Host Institution: UCF

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