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Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging
[Image: see text] The photolysis of acetylacetone (AcAc) has been studied using velocity-map ion imaging with pulsed nanosecond lasers. The enolone tautomer of AcAc (CH(3)C(O)CH=C(OH)CH(3)) was excited in the strong UV absorption band by UV pulses at 280 nm, preparing the S(2)(ππ*) state, and produc...
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
American Chemical Society
2023
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10440790/ https://www.ncbi.nlm.nih.gov/pubmed/37535453 http://dx.doi.org/10.1021/acs.jpca.3c01653 |
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author | Rinaman, Johanna E. Murray, Craig |
author_facet | Rinaman, Johanna E. Murray, Craig |
author_sort | Rinaman, Johanna E. |
collection | PubMed |
description | [Image: see text] The photolysis of acetylacetone (AcAc) has been studied using velocity-map ion imaging with pulsed nanosecond lasers. The enolone tautomer of AcAc (CH(3)C(O)CH=C(OH)CH(3)) was excited in the strong UV absorption band by UV pulses at 280 nm, preparing the S(2)(ππ*) state, and products were probed after a short time delay by single-photon VUV ionization at 118.2 nm. Two-color UV + VUV time-of-flight mass spectra show enhancement of fragments at m/z = 15, 42, 43, 58, and 85 at the lowest UV pulse energies and depletion of the parent ion at m/z = 100. Ion images of the five major fragments are all isotropic, indicating dissociation lifetimes that are long on the timescale of molecular rotation but shorter than the laser pulse duration (<6 ns). The m/z = 15 and 85 fragments have identical momentum distributions with moderate translational energy release, suggesting that they are formed as a neutral product pair and likely via a Norrish type I dissociation of the enolone to form CH(3) + C(O)CH=C(OH)CH(3) over a barrier on a triplet surface. The m/z = 43 fragment may be tentatively assigned to the alternative Norrish type I pathway that produces CH(3)CO + CH(2)C(O)CH(3) on S(0) following phototautomerization to the diketone, although alternative mechanisms involving dissociative ionization of a larger primary photoproduct cannot be conclusively ruled out. The m/z = 42 and 58 fragments are not momentum-matched and consequently are not formed as a neutral pair via a unimolecular dissociation pathway on S(0). They also likely originate from the dissociative ionization of primary photofragments. RRKM calculations suggest that unimolecular dissociation pathways that lead to molecular products on S(0) are generally slow, implying an upper-limit lifetime of <46 ns after excitation at 280 nm. Time-dependent measurements suggest that the observed photofragments likely do not arise from dissociative ionization of energized AcAc S(0)*. |
format | Online Article Text |
id | pubmed-10440790 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2023 |
publisher | American Chemical Society |
record_format | MEDLINE/PubMed |
spelling | pubmed-104407902023-08-22 Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging Rinaman, Johanna E. Murray, Craig J Phys Chem A [Image: see text] The photolysis of acetylacetone (AcAc) has been studied using velocity-map ion imaging with pulsed nanosecond lasers. The enolone tautomer of AcAc (CH(3)C(O)CH=C(OH)CH(3)) was excited in the strong UV absorption band by UV pulses at 280 nm, preparing the S(2)(ππ*) state, and products were probed after a short time delay by single-photon VUV ionization at 118.2 nm. Two-color UV + VUV time-of-flight mass spectra show enhancement of fragments at m/z = 15, 42, 43, 58, and 85 at the lowest UV pulse energies and depletion of the parent ion at m/z = 100. Ion images of the five major fragments are all isotropic, indicating dissociation lifetimes that are long on the timescale of molecular rotation but shorter than the laser pulse duration (<6 ns). The m/z = 15 and 85 fragments have identical momentum distributions with moderate translational energy release, suggesting that they are formed as a neutral product pair and likely via a Norrish type I dissociation of the enolone to form CH(3) + C(O)CH=C(OH)CH(3) over a barrier on a triplet surface. The m/z = 43 fragment may be tentatively assigned to the alternative Norrish type I pathway that produces CH(3)CO + CH(2)C(O)CH(3) on S(0) following phototautomerization to the diketone, although alternative mechanisms involving dissociative ionization of a larger primary photoproduct cannot be conclusively ruled out. The m/z = 42 and 58 fragments are not momentum-matched and consequently are not formed as a neutral pair via a unimolecular dissociation pathway on S(0). They also likely originate from the dissociative ionization of primary photofragments. RRKM calculations suggest that unimolecular dissociation pathways that lead to molecular products on S(0) are generally slow, implying an upper-limit lifetime of <46 ns after excitation at 280 nm. Time-dependent measurements suggest that the observed photofragments likely do not arise from dissociative ionization of energized AcAc S(0)*. American Chemical Society 2023-08-03 /pmc/articles/PMC10440790/ /pubmed/37535453 http://dx.doi.org/10.1021/acs.jpca.3c01653 Text en © 2023 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/). |
spellingShingle | Rinaman, Johanna E. Murray, Craig Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging |
title | Acetylacetone Photolysis
at 280 nm Studied by Velocity-Map
Ion Imaging |
title_full | Acetylacetone Photolysis
at 280 nm Studied by Velocity-Map
Ion Imaging |
title_fullStr | Acetylacetone Photolysis
at 280 nm Studied by Velocity-Map
Ion Imaging |
title_full_unstemmed | Acetylacetone Photolysis
at 280 nm Studied by Velocity-Map
Ion Imaging |
title_short | Acetylacetone Photolysis
at 280 nm Studied by Velocity-Map
Ion Imaging |
title_sort | acetylacetone photolysis
at 280 nm studied by velocity-map
ion imaging |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10440790/ https://www.ncbi.nlm.nih.gov/pubmed/37535453 http://dx.doi.org/10.1021/acs.jpca.3c01653 |
work_keys_str_mv | AT rinamanjohannae acetylacetonephotolysisat280nmstudiedbyvelocitymapionimaging AT murraycraig acetylacetonephotolysisat280nmstudiedbyvelocitymapionimaging |