TY - JOUR
T1 - Singlet O2Produced by Ultraviolet Dissociation of the β-ionone-O2Complex
AU - Parsons, Bradley F.
AU - Freitag, Mark A.
AU - Warder, Hunter J.
N1 - Funding Information:
The authors express appreciation for financial assistance from the Betty and Donald J. Baumann Family Fund for Research and Outreach as well as the College of Arts and Sciences and the Department of Chemistry and Biochemistry at Creighton University. Computational resources were provided by the RaDLab High Performance Computing project at Creighton University. Finally, the authors would like to thank Professor David Szpunar at the University of Wisconsin at Stevens-Point for providing feedback on this manuscript and very fruitful discussions.
Publisher Copyright:
© 2021 American Chemical Society
PY - 2021/10/7
Y1 - 2021/10/7
N2 - We formed the gas-phase β-ionone-O2complex in a supersonic expansion and then photodissociated the complex with light near 312 nm. Photodissociation resulted in the production of O2in the a1Δgstate, which was ionized at 312 nm using (2 + 1) resonance-enhanced multiphoton ionization (REMPI). We recorded the1O2REMPI action spectrum and O2+velocity map ion image following photodissociation of the complex. From the velocity map image, we determined the total recoil kinetic energy distribution from dissociation of the complex. Fitting the REMPI spectrum showed that the1O2product has an effective rotational temperature of about 50 K, while the recoil kinetic energy distribution was well fit with a statistical Boltzmann distribution having an effective translational temperature of 289 K. Using the average translational energy from the Boltzmann fit along with the complex dissociation energy fromab initiocalculations, we determined that β-ionone was formed with an average of 2.87 eV of internal energy, which was 0.49 eV higher than previous measurements for the β-ionone triplet-state energy. Our own CCSD/cc-pVDZ//(U)MP2/cc-pVDZ calculations gave a minimum triplet-state energy of 2.04 eV. However, a large structural change occurs between the minimum singlet-ground-state geometry and the minimum triplet-excited-state geometry, and as a result, the calculated vertical energy for the triplet-state β-ionone was determined to be 3.30 eV. Comparing theab initioand experimental results indicated that following excitation, β-ionone was formed in the triplet state but with significant internal vibrational energy. As such, complex dissociation likely proceeds following internal vibrational energy redistribution, which explains the statistical recoil kinetic energy distribution.
AB - We formed the gas-phase β-ionone-O2complex in a supersonic expansion and then photodissociated the complex with light near 312 nm. Photodissociation resulted in the production of O2in the a1Δgstate, which was ionized at 312 nm using (2 + 1) resonance-enhanced multiphoton ionization (REMPI). We recorded the1O2REMPI action spectrum and O2+velocity map ion image following photodissociation of the complex. From the velocity map image, we determined the total recoil kinetic energy distribution from dissociation of the complex. Fitting the REMPI spectrum showed that the1O2product has an effective rotational temperature of about 50 K, while the recoil kinetic energy distribution was well fit with a statistical Boltzmann distribution having an effective translational temperature of 289 K. Using the average translational energy from the Boltzmann fit along with the complex dissociation energy fromab initiocalculations, we determined that β-ionone was formed with an average of 2.87 eV of internal energy, which was 0.49 eV higher than previous measurements for the β-ionone triplet-state energy. Our own CCSD/cc-pVDZ//(U)MP2/cc-pVDZ calculations gave a minimum triplet-state energy of 2.04 eV. However, a large structural change occurs between the minimum singlet-ground-state geometry and the minimum triplet-excited-state geometry, and as a result, the calculated vertical energy for the triplet-state β-ionone was determined to be 3.30 eV. Comparing theab initioand experimental results indicated that following excitation, β-ionone was formed in the triplet state but with significant internal vibrational energy. As such, complex dissociation likely proceeds following internal vibrational energy redistribution, which explains the statistical recoil kinetic energy distribution.
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U2 - 10.1021/acs.jpca.1c06669
DO - 10.1021/acs.jpca.1c06669
M3 - Article
C2 - 34554753
AN - SCOPUS:85116522160
VL - 125
SP - 8649
EP - 8657
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 39
ER -