Collisional and photoexcitation of transition metal clusters
<p>The properties of transition metal clusters differ from those of both atomic and bulk size regimes. Such clusters are incompletely understood and potentially useful, making them attractive targets for further study.</p> <p>The very smallest clusters studied in this thesis (CuO,...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2014
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| _version_ | 1797109871029518336 |
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| author | Parry, I |
| author2 | Mackenzie, S |
| author_facet | Mackenzie, S Parry, I |
| author_sort | Parry, I |
| collection | OXFORD |
| description | <p>The properties of transition metal clusters differ from those of both atomic and bulk size regimes. Such clusters are incompletely understood and potentially useful, making them attractive targets for further study.</p> <p>The very smallest clusters studied in this thesis (CuO, Cu<sub>2</sub> and Cu<sub>3</sub>) have been investigated with velocity map imaging. 1+1' photodissociation of CuO X <sup>2</sup>Π<sub>3/2</sub> was observed, via the C, D, E, F and H states of CuO. CuO&ast; was photodissociated to form Cu(<sup>2</sup>D<sub>3/2</sub>) + O(<sup>1</sup>D<sub>2</sub>). D<sub>0</sub>(CuO) was determined to be 3.041±0.030 cm<sup>-1</sup>. Non-resonant three-photon Cu<sub>2</sub> photodissociation occurred throughout the energy range studied to produce one ground-state and one highly-excited copper atom,Cu&ast;. Cu&ast; was ionised by a single additional visible photon. Nearly all Cu&ast; atoms with internal energies between 41000 and 53000 cm<sup>-1</sup> were observed. D<sub>0</sub>(Cu<sub>2</sub>) has been calculated to be 1.992±0.037 eV. </p> <p>Features arising from photodissociation of Cu<sub>3</sub> were observed in the Cu<sup>&plus;</sup> and Cu<sub>2</sub><sup>&plus;</sup> ion yield spectra and images. Their structure was ill-resolved due to uncertainties in the internal energy of both parent Cu<sub>3</sub> and product Cu<sub>2</sub>. These features correspond to single-photon dissociation of Cu<sub>3</sub> to produce metastable D-states of the copper atom and vibrationally excited Cu<sub>2</sub>. One series of features implies a previously-unobserved state of either Cu<sub>2</sub> or Cu<sub>3</sub>.</p> <p>Rh<sub>n</sub>N<sub>2</sub>O<sup>&plus;</sup> and Rh<sub>n</sub>ON<sub>2</sub>O<sup>&plus;</sup> (n=5, 6) were collisionally activated in collision-induced dissociation (CID) experiments with Ar and <sup>13</sup>CO. These experiments were carried out in a Fourier Transform Ion Cyclotron Resonance(FT-ICR)spectrometer. Argon collisions induced both N<sub>2</sub>O desorption and N<sub>2</sub>O reduction. The branching ratios observed reproduced those seen in prior IR-MPD experiments. <sup>13</sup>CO was observed to chemisorb to the cluster upon collision, activating not only N<sub>2</sub>O desorption and reduction but also CO oxidation. Formation of CO2 was noted to be particularly rapid on the n=5 cluster compared to the n=6 cluster.</p> <p>Reactions of Rh<sub>n</sub>N<sub>2</sub>O<sup>&plus;</sup> (n=4-6) clusters were also activated by black body radiation. This technique is known as BIRD - black-body induced infrared radiative dissociation. These studies revealed that the N<sub>2</sub>O desorption barrier exceeds the N<sub>2</sub>O reduction barrier on all clusters studied, but that the entropic favourability of desorption increases its rate relative to reduction with increasing cluster internal energy. The BIRD rate was much reduced upon cooling the ICR cell to 100 K. A further test of the BIRD mechanism increased the number of N<sub>2</sub>O ligands and hence the absorption rate. An approximately linear increase in the dissociation rate of Rh<sub>n</sub>(N<sub>2</sub>O)<sub>m</sub><sup>&plus;</sup> was observed with index m. Deviations from linearity were caused by variations in the N<sub>2</sub>O desorption rate. In the case of Rh<sub>5</sub>(N<sub>2</sub>O)<sub>m</sub><sup>&plus;</sup>, desorption rates corresponded closely to N<sub>2</sub>O binding energies calculated by density functional theory. The system was modelled using a master equation approach.</p> |
| first_indexed | 2024-03-07T07:47:22Z |
| format | Thesis |
| id | oxford-uuid:b1f2fc37-97ff-4500-ab34-ceb7e515b9d2 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T07:47:22Z |
| publishDate | 2014 |
| record_format | dspace |
| spelling | oxford-uuid:b1f2fc37-97ff-4500-ab34-ceb7e515b9d22023-06-14T08:01:36ZCollisional and photoexcitation of transition metal clustersThesishttp://purl.org/coar/resource_type/c_db06uuid:b1f2fc37-97ff-4500-ab34-ceb7e515b9d2Physical & theoretical chemistryEnglishOxford University Research Archive - Valet2014Parry, IMackenzie, S<p>The properties of transition metal clusters differ from those of both atomic and bulk size regimes. Such clusters are incompletely understood and potentially useful, making them attractive targets for further study.</p> <p>The very smallest clusters studied in this thesis (CuO, Cu<sub>2</sub> and Cu<sub>3</sub>) have been investigated with velocity map imaging. 1+1' photodissociation of CuO X <sup>2</sup>Π<sub>3/2</sub> was observed, via the C, D, E, F and H states of CuO. CuO&ast; was photodissociated to form Cu(<sup>2</sup>D<sub>3/2</sub>) + O(<sup>1</sup>D<sub>2</sub>). D<sub>0</sub>(CuO) was determined to be 3.041±0.030 cm<sup>-1</sup>. Non-resonant three-photon Cu<sub>2</sub> photodissociation occurred throughout the energy range studied to produce one ground-state and one highly-excited copper atom,Cu&ast;. Cu&ast; was ionised by a single additional visible photon. Nearly all Cu&ast; atoms with internal energies between 41000 and 53000 cm<sup>-1</sup> were observed. D<sub>0</sub>(Cu<sub>2</sub>) has been calculated to be 1.992±0.037 eV. </p> <p>Features arising from photodissociation of Cu<sub>3</sub> were observed in the Cu<sup>&plus;</sup> and Cu<sub>2</sub><sup>&plus;</sup> ion yield spectra and images. Their structure was ill-resolved due to uncertainties in the internal energy of both parent Cu<sub>3</sub> and product Cu<sub>2</sub>. These features correspond to single-photon dissociation of Cu<sub>3</sub> to produce metastable D-states of the copper atom and vibrationally excited Cu<sub>2</sub>. One series of features implies a previously-unobserved state of either Cu<sub>2</sub> or Cu<sub>3</sub>.</p> <p>Rh<sub>n</sub>N<sub>2</sub>O<sup>&plus;</sup> and Rh<sub>n</sub>ON<sub>2</sub>O<sup>&plus;</sup> (n=5, 6) were collisionally activated in collision-induced dissociation (CID) experiments with Ar and <sup>13</sup>CO. These experiments were carried out in a Fourier Transform Ion Cyclotron Resonance(FT-ICR)spectrometer. Argon collisions induced both N<sub>2</sub>O desorption and N<sub>2</sub>O reduction. The branching ratios observed reproduced those seen in prior IR-MPD experiments. <sup>13</sup>CO was observed to chemisorb to the cluster upon collision, activating not only N<sub>2</sub>O desorption and reduction but also CO oxidation. Formation of CO2 was noted to be particularly rapid on the n=5 cluster compared to the n=6 cluster.</p> <p>Reactions of Rh<sub>n</sub>N<sub>2</sub>O<sup>&plus;</sup> (n=4-6) clusters were also activated by black body radiation. This technique is known as BIRD - black-body induced infrared radiative dissociation. These studies revealed that the N<sub>2</sub>O desorption barrier exceeds the N<sub>2</sub>O reduction barrier on all clusters studied, but that the entropic favourability of desorption increases its rate relative to reduction with increasing cluster internal energy. The BIRD rate was much reduced upon cooling the ICR cell to 100 K. A further test of the BIRD mechanism increased the number of N<sub>2</sub>O ligands and hence the absorption rate. An approximately linear increase in the dissociation rate of Rh<sub>n</sub>(N<sub>2</sub>O)<sub>m</sub><sup>&plus;</sup> was observed with index m. Deviations from linearity were caused by variations in the N<sub>2</sub>O desorption rate. In the case of Rh<sub>5</sub>(N<sub>2</sub>O)<sub>m</sub><sup>&plus;</sup>, desorption rates corresponded closely to N<sub>2</sub>O binding energies calculated by density functional theory. The system was modelled using a master equation approach.</p> |
| spellingShingle | Physical & theoretical chemistry Parry, I Collisional and photoexcitation of transition metal clusters |
| title | Collisional and photoexcitation of transition metal clusters |
| title_full | Collisional and photoexcitation of transition metal clusters |
| title_fullStr | Collisional and photoexcitation of transition metal clusters |
| title_full_unstemmed | Collisional and photoexcitation of transition metal clusters |
| title_short | Collisional and photoexcitation of transition metal clusters |
| title_sort | collisional and photoexcitation of transition metal clusters |
| topic | Physical & theoretical chemistry |
| work_keys_str_mv | AT parryi collisionalandphotoexcitationoftransitionmetalclusters |