A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase
<p>Vibrational excitation of molecules prior to collision and subsequent reaction can change the outcome of the reaction by either enhancing or diminishing reaction rates or even changing product distributions. Studies of the effects of vibrational excitation on reactive outcomes have been li...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
2023
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| Subjects: |
| _version_ | 1797111551323275264 |
|---|---|
| author | Brewer, EI |
| author2 | Mackenzie, S |
| author_facet | Mackenzie, S Brewer, EI |
| author_sort | Brewer, EI |
| collection | OXFORD |
| description | <p>Vibrational excitation of molecules prior to collision and subsequent reaction can change the outcome of the reaction by either enhancing or diminishing reaction rates or even changing product distributions.
Studies of the effects of vibrational excitation on reactive outcomes have been limited to extremely simple gas phase systems or extended metal surfaces.
The first part of this thesis details the design, development and construction of a new instrument to study the effects of vibrational excitation on the reactions of ionic metals species (single atoms or clusters) reacting with neutral species in the gas phase.
Starting from a collision cell designed from a simple theoretical model of collisions, a tandem ToF mass spectrometer was designed from scratch to collide ionic metal species with single neutral gas molecules with controlled energies and good spatial focus prior to detection of the collision products.
Laser ablation sources provide very poorly spatially and energetically resolved ion packets requiring extensive ion optics to control them.
While the instrument development is still ongoing, due to difficulties associated with controlling ion kinetic energies and maintaining good transmission, an instrument capable of carrying out reactive collisions has been successfully developed. </p>
<p>The second part of the thesis presents infrared multi-photon dissociation spectroscopic studies
of Ho<sup>+</sup> cations with CO<sub>2</sub> and OCS molecules. Both Ho(CO<sub>2</sub> )<sup>+</sup><sub>n</sub> and Ho[O(CO<sub>2</sub>)<sub>n</sub>]<sup>+</sup> are obtained
when Ho is ablated in the presence of CO<sub>2</sub> seeded into Ar. Spectra were recorded in two spectral
ranges: 1650-1950 cm<sup>−1</sup> and 2300-2450 cm<sup>−1</sup> and assigned using predicted structures (generated
from potential energy surface searches) using density functional theory (DFT). CO<sub>2</sub> binds in a
molecular/end-on fashion to Ho<sup>+</sup> in Ho(CO<sub>2</sub>)<sup>+</sup>n complexes and showed little evidence of activation.
Ho[O(CO<sub>2</sub>)<sub>n</sub>]<sup>+</sup> complexes in which n ≥ 3, by contrast, show clear spectroscopic evidence
of the formation of a carbonate radical anion moiety ({CO<sub>3</sub>}<sup>·δ−</sup>). The characteristic vibrational
band of this structure red-shifts with increasing CO<sub>2</sub> coordination displaying clear evidence of
charge transfer between ligands mediated by a metal centre. Ho[(OCS)<sub>n</sub>]<sup>+</sup>, Ho[S(OCS)<sub>n</sub>]<sup>+</sup> and
Ho[O(OCS)<sub>n</sub>]<sup>+</sup> complexes, are generated when Ho is ablated in the presence of OCS seeded
into and He. Spectra of each molecule were recorded between 1200-2400 cm<sup>−1</sup> and assigned
based on DFT calculations. OCS was found to react with Ho<sup>+</sup> ions to form both HoO<sup>+</sup> +
CS and HoS<sup>+</sup> + CO as well as bind in a molecular fashion analogous to CO<sub>2</sub>. Both HoO<sup>+</sup>
and HoS<sup>+</sup> were observed to produce {CO<sub>2</sub> S}<sup>·δ−</sup> and {COS<sub>2</sub> }<sup>·δ−</sup> respectively that preferentially
bound to the Ho<sup>+</sup> via sulphur atoms. The COS<sub>2</sub> C=O bond stretch is observed to red-shift
with increasing complex size illustrating that additional OCS ligands donate electron density
to stabilise the thiocarbonate in an identical fashion to the behaviour seen in Ho[O(CO<sub>2</sub> 2)<sub>n</sub>]<sup>+</sup>
species.</p> |
| first_indexed | 2024-03-07T08:10:25Z |
| format | Thesis |
| id | oxford-uuid:f69ddd41-bcb0-4acd-a577-49ca934af957 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T08:10:25Z |
| publishDate | 2023 |
| record_format | dspace |
| spelling | oxford-uuid:f69ddd41-bcb0-4acd-a577-49ca934af9572023-11-21T10:35:03ZA new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phaseThesishttp://purl.org/coar/resource_type/c_db06uuid:f69ddd41-bcb0-4acd-a577-49ca934af957Collsion dynamicsReaction dynamicsClustersInfrared photodissociation spectroscopyVibrationally enhanced chemistryMode selective chemistryVibrational spectroscopyNovel instrumentEnglishHyrax Deposit2023Brewer, EIMackenzie, SVallance, CHeazlewood, B<p>Vibrational excitation of molecules prior to collision and subsequent reaction can change the outcome of the reaction by either enhancing or diminishing reaction rates or even changing product distributions. Studies of the effects of vibrational excitation on reactive outcomes have been limited to extremely simple gas phase systems or extended metal surfaces. The first part of this thesis details the design, development and construction of a new instrument to study the effects of vibrational excitation on the reactions of ionic metals species (single atoms or clusters) reacting with neutral species in the gas phase. Starting from a collision cell designed from a simple theoretical model of collisions, a tandem ToF mass spectrometer was designed from scratch to collide ionic metal species with single neutral gas molecules with controlled energies and good spatial focus prior to detection of the collision products. Laser ablation sources provide very poorly spatially and energetically resolved ion packets requiring extensive ion optics to control them. While the instrument development is still ongoing, due to difficulties associated with controlling ion kinetic energies and maintaining good transmission, an instrument capable of carrying out reactive collisions has been successfully developed. </p> <p>The second part of the thesis presents infrared multi-photon dissociation spectroscopic studies of Ho<sup>+</sup> cations with CO<sub>2</sub> and OCS molecules. Both Ho(CO<sub>2</sub> )<sup>+</sup><sub>n</sub> and Ho[O(CO<sub>2</sub>)<sub>n</sub>]<sup>+</sup> are obtained when Ho is ablated in the presence of CO<sub>2</sub> seeded into Ar. Spectra were recorded in two spectral ranges: 1650-1950 cm<sup>−1</sup> and 2300-2450 cm<sup>−1</sup> and assigned using predicted structures (generated from potential energy surface searches) using density functional theory (DFT). CO<sub>2</sub> binds in a molecular/end-on fashion to Ho<sup>+</sup> in Ho(CO<sub>2</sub>)<sup>+</sup>n complexes and showed little evidence of activation. Ho[O(CO<sub>2</sub>)<sub>n</sub>]<sup>+</sup> complexes in which n ≥ 3, by contrast, show clear spectroscopic evidence of the formation of a carbonate radical anion moiety ({CO<sub>3</sub>}<sup>·δ−</sup>). The characteristic vibrational band of this structure red-shifts with increasing CO<sub>2</sub> coordination displaying clear evidence of charge transfer between ligands mediated by a metal centre. Ho[(OCS)<sub>n</sub>]<sup>+</sup>, Ho[S(OCS)<sub>n</sub>]<sup>+</sup> and Ho[O(OCS)<sub>n</sub>]<sup>+</sup> complexes, are generated when Ho is ablated in the presence of OCS seeded into and He. Spectra of each molecule were recorded between 1200-2400 cm<sup>−1</sup> and assigned based on DFT calculations. OCS was found to react with Ho<sup>+</sup> ions to form both HoO<sup>+</sup> + CS and HoS<sup>+</sup> + CO as well as bind in a molecular fashion analogous to CO<sub>2</sub>. Both HoO<sup>+</sup> and HoS<sup>+</sup> were observed to produce {CO<sub>2</sub> S}<sup>·δ−</sup> and {COS<sub>2</sub> }<sup>·δ−</sup> respectively that preferentially bound to the Ho<sup>+</sup> via sulphur atoms. The COS<sub>2</sub> C=O bond stretch is observed to red-shift with increasing complex size illustrating that additional OCS ligands donate electron density to stabilise the thiocarbonate in an identical fashion to the behaviour seen in Ho[O(CO<sub>2</sub> 2)<sub>n</sub>]<sup>+</sup> species.</p> |
| spellingShingle | Collsion dynamics Reaction dynamics Clusters Infrared photodissociation spectroscopy Vibrationally enhanced chemistry Mode selective chemistry Vibrational spectroscopy Novel instrument Brewer, EI A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title | A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title_full | A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title_fullStr | A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title_full_unstemmed | A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title_short | A new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| title_sort | new instrument to study vibrationally enhanced chemistry on metal clusters in the gas phase |
| topic | Collsion dynamics Reaction dynamics Clusters Infrared photodissociation spectroscopy Vibrationally enhanced chemistry Mode selective chemistry Vibrational spectroscopy Novel instrument |
| work_keys_str_mv | AT brewerei anewinstrumenttostudyvibrationallyenhancedchemistryonmetalclustersinthegasphase AT brewerei newinstrumenttostudyvibrationallyenhancedchemistryonmetalclustersinthegasphase |