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Title: To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone

Abstract

We investigate the gas-phase photochemistry of the enolone tautomer of acetylacetone (pentane-2,4-dione) following S2(ππ*) ← S o excitation at λ = 266 and 248 nm, using three complementary time-resolved spectroscopic methods. Contrary to earlier reports, which claimed to study 1-photon excitation of acetylacetone and found OH and CH 3 as the only important gas-phase products, we detect fifteen unique primary photoproducts and demonstrate that five of them, including OH and CH 3, arise solely by multiphoton excitation. We assign the 1-photon products to six photochemical channels and show that the most significant pathway is tautomerization to the diketone form, which is likely an intermediate in several of the other product channels. Furthermore, we measure the equilibrium constant of this keto-enol tautomerization on S0 from 320 to 600 K and extract ΔH = 4.1 ± 0.3 kcal∙mol –1, and ΔS = 6.8 ± 0.5 cal∙mol –1∙K –1 using a van’t Hoff analysis. We correct the C–OH bond dissociation energy in acetylacetone, previously determined as 90 kcal∙mol –1 by theory and experiment, to a new value of 121.7 kcal∙mol –1. Here, our experiments and electronic structure calculations provide evidence that some of the product channels, including phototautomerization, occur on S o, whilemore » others likely occur on excited triplet surfaces. Although the strong oscillator strength of the S 2 ← S o transition results from the (ππ*) excitation of the C=C–C=O backbone, similar to conjugated polyenes, the participation of triplets in the dissociation pathways of acetylacetone appears to have more in common with ketone photochemistry.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [5];  [1];  [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Univ. of the Pacific, Stockton, CA (United States); Univ. of Nevada, Reno, NV (United States)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States); KLA-Tencor Corp., Milpitas, CA (United States)
  4. Univ. of the Pacific, Stockton, CA (United States)
  5. Paul Scherrer Inst. (PSI), Villigen (Switzerland)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1528999
Report Number(s):
SAND-2019-3492J
Journal ID: ISSN 1089-5639; 673899
Grant/Contract Number:  
AC04-94AL85000
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Antonov, Ivan O., Voronova, Krisztina, Chen, Ming -Wei, Sztaray, Balint, Hemberger, Patrick, Bodi, Andras, Osborn, David L., and Sheps, Leonid. To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone. United States: N. p., 2019. Web. doi:10.1021/acs.jpca.9b04640.
Antonov, Ivan O., Voronova, Krisztina, Chen, Ming -Wei, Sztaray, Balint, Hemberger, Patrick, Bodi, Andras, Osborn, David L., & Sheps, Leonid. To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone. United States. doi:10.1021/acs.jpca.9b04640.
Antonov, Ivan O., Voronova, Krisztina, Chen, Ming -Wei, Sztaray, Balint, Hemberger, Patrick, Bodi, Andras, Osborn, David L., and Sheps, Leonid. Wed . "To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone". United States. doi:10.1021/acs.jpca.9b04640.
@article{osti_1528999,
title = {To Boldly Look Where No One Has Looked Before: Identifying the Primary Photoproducts of Acetylacetone},
author = {Antonov, Ivan O. and Voronova, Krisztina and Chen, Ming -Wei and Sztaray, Balint and Hemberger, Patrick and Bodi, Andras and Osborn, David L. and Sheps, Leonid},
abstractNote = {We investigate the gas-phase photochemistry of the enolone tautomer of acetylacetone (pentane-2,4-dione) following S2(ππ*) ← So excitation at λ = 266 and 248 nm, using three complementary time-resolved spectroscopic methods. Contrary to earlier reports, which claimed to study 1-photon excitation of acetylacetone and found OH and CH3 as the only important gas-phase products, we detect fifteen unique primary photoproducts and demonstrate that five of them, including OH and CH3, arise solely by multiphoton excitation. We assign the 1-photon products to six photochemical channels and show that the most significant pathway is tautomerization to the diketone form, which is likely an intermediate in several of the other product channels. Furthermore, we measure the equilibrium constant of this keto-enol tautomerization on S0 from 320 to 600 K and extract ΔH = 4.1 ± 0.3 kcal∙mol–1, and ΔS = 6.8 ± 0.5 cal∙mol–1∙K–1 using a van’t Hoff analysis. We correct the C–OH bond dissociation energy in acetylacetone, previously determined as 90 kcal∙mol–1 by theory and experiment, to a new value of 121.7 kcal∙mol–1. Here, our experiments and electronic structure calculations provide evidence that some of the product channels, including phototautomerization, occur on So, while others likely occur on excited triplet surfaces. Although the strong oscillator strength of the S2 ← So transition results from the (ππ*) excitation of the C=C–C=O backbone, similar to conjugated polyenes, the participation of triplets in the dissociation pathways of acetylacetone appears to have more in common with ketone photochemistry.},
doi = {10.1021/acs.jpca.9b04640},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {6}
}

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