Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation.
Reaction pathways that bypass the conventional saddle-point transition state (TS) are of considerable interest and importance. An example of such a pathway, termed "roaming," has been described in the photodissociation of H(2)CO. In a combined experimental and theoretical study, we show th...
| Main Authors: | , , , , , , , |
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| Format: | Journal article |
| Sprog: | English |
| Udgivet: |
2008
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| _version_ | 1826291894702833664 |
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| author | Heazlewood, B Jordan, M Kable, S Selby, T Osborn, D Shepler, B Braams, B Bowman, J |
| author_facet | Heazlewood, B Jordan, M Kable, S Selby, T Osborn, D Shepler, B Braams, B Bowman, J |
| author_sort | Heazlewood, B |
| collection | OXFORD |
| description | Reaction pathways that bypass the conventional saddle-point transition state (TS) are of considerable interest and importance. An example of such a pathway, termed "roaming," has been described in the photodissociation of H(2)CO. In a combined experimental and theoretical study, we show that roaming pathways are important in the 308-nm photodissociation of CH(3)CHO to CH(4) + CO. The CH(4) product is found to have extreme vibrational excitation, with the vibrational distribution peaked at approximately 95% of the total available energy. Quasiclassical trajectory calculations on full-dimensional potential energy surfaces reproduce these results and are used to infer that the major route to CH(4) + CO products is via a roaming pathway where a CH(3) fragment abstracts an H from HCO. The conventional saddle-point TS pathway to CH(4) + CO formation plays only a minor role. H-atom roaming is also observed, but this is also a minor pathway. The dominance of the CH(3) roaming mechanism is attributed to the fact that the CH(3) + HCO radical asymptote and the TS saddle-point barrier to CH(4) + CO are nearly isoenergetic. Roaming dynamics are therefore not restricted to small molecules such as H(2)CO, nor are they limited to H atoms being the roaming fragment. The observed dominance of the roaming mechanism over the conventional TS mechanism presents a significant challenge to current reaction rate theory. |
| first_indexed | 2024-03-07T03:06:21Z |
| format | Journal article |
| id | oxford-uuid:b2aba41e-74c9-48c7-bfab-dfa591e336d6 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T03:06:21Z |
| publishDate | 2008 |
| record_format | dspace |
| spelling | oxford-uuid:b2aba41e-74c9-48c7-bfab-dfa591e336d62022-03-27T04:13:21ZRoaming is the dominant mechanism for molecular products in acetaldehyde photodissociation.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:b2aba41e-74c9-48c7-bfab-dfa591e336d6EnglishSymplectic Elements at Oxford2008Heazlewood, BJordan, MKable, SSelby, TOsborn, DShepler, BBraams, BBowman, JReaction pathways that bypass the conventional saddle-point transition state (TS) are of considerable interest and importance. An example of such a pathway, termed "roaming," has been described in the photodissociation of H(2)CO. In a combined experimental and theoretical study, we show that roaming pathways are important in the 308-nm photodissociation of CH(3)CHO to CH(4) + CO. The CH(4) product is found to have extreme vibrational excitation, with the vibrational distribution peaked at approximately 95% of the total available energy. Quasiclassical trajectory calculations on full-dimensional potential energy surfaces reproduce these results and are used to infer that the major route to CH(4) + CO products is via a roaming pathway where a CH(3) fragment abstracts an H from HCO. The conventional saddle-point TS pathway to CH(4) + CO formation plays only a minor role. H-atom roaming is also observed, but this is also a minor pathway. The dominance of the CH(3) roaming mechanism is attributed to the fact that the CH(3) + HCO radical asymptote and the TS saddle-point barrier to CH(4) + CO are nearly isoenergetic. Roaming dynamics are therefore not restricted to small molecules such as H(2)CO, nor are they limited to H atoms being the roaming fragment. The observed dominance of the roaming mechanism over the conventional TS mechanism presents a significant challenge to current reaction rate theory. |
| spellingShingle | Heazlewood, B Jordan, M Kable, S Selby, T Osborn, D Shepler, B Braams, B Bowman, J Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title | Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title_full | Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title_fullStr | Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title_full_unstemmed | Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title_short | Roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation. |
| title_sort | roaming is the dominant mechanism for molecular products in acetaldehyde photodissociation |
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