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Origin of the "odd" behavior in the ultraviolet photochemistry of ozone. Proc Natl Acad Sci U S A 2020; 117:21065-21069. [PMID: 32817468 DOI: 10.1073/pnas.2006070117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The origin of the even-odd rotational state population alternation in the 16O2(a 1Δg) fragments resulting from the ultraviolet (UV) photodissociation of 16O3, a phenomenon first observed over 30 years ago, has been elucidated using full quantum theory. The calculated 16O2(a 1Δg) rotational state distribution following the 266-nm photolysis of 60 K ozone shows a strong even-odd propensity, in excellent agreement with the new experimental rotational state distribution measured under the same conditions. Theory indicates that the even rotational states are significantly more populated than the adjacent odd rotational states because of a preference for the formation of the A' Λ-doublet, which can only occupy even rotational states due to the exchange symmetry of the two bosonic 16O nuclei, and thus not as a result of parity-selective curve crossing as previously proposed. For nonrotating ozone, its dissociation on the excited B1A' state dictates that only A' Λ-doublets are populated, due to symmetry conservation. This selection rule is relaxed for rotating parent molecules, but a preference still persists for A' Λ-doublets. The A''/A' ratio increases with increasing ozone rotational quantum number, and thus with increasing temperature, explaining the previously observed temperature dependence of the even-odd population alternation. In light of these results, it is concluded that the previously proposed parity-selective curve-crossing mechanism cannot be a source of heavy isotopic enrichment in the atmosphere.
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Gunthardt CE, Aardema MN, Hall GE, North SW. Evidence for lambda doublet propensity in the UV photodissociation of ozone. J Chem Phys 2019; 151:224302. [PMID: 31837678 DOI: 10.1063/1.5131504] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The photodissociation of O3 at 266 nm has been studied using velocity mapped ion imaging. We report temperature-dependent vector correlations for the O2(a1Δg, v = 0, j = 18-20) fragments at molecular beam temperatures of 70 K, 115 K, and 170 K. Both the fragment spatial anisotropy and the v-j correlations are found to be increasingly depolarized with increasing beam temperature. At all temperatures, the v-j correlations for the j = 19 state were shown to be reduced compared to those of j = 18 and 20, while no such odd/even rotational state difference was observed for the spatial anisotropy, consistent with previous measurements. We find that temperature-dependent differences in the populations and v-j correlations between the odd and even rotational states can be explained by a Λ-doublet propensity model. Although symmetry conservation should lead to formation of only the A' Λ-doublet component, and only even rotational states, out-of-plane rotation of the parent molecule breaks the planar symmetry and permits the formation of the A″ Λ-doublet component and odd rotational states. A simple classical model to treat the effect of parent rotation on the v-j correlation and the odd/even rotational population alternation reproduces both the current measurements and previously reported rotational distributions, suggesting that the "odd" behavior originates from a Λ-doublet propensity, and not from a mass independent curve crossing effect, as previously proposed.
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Affiliation(s)
- Carolyn E Gunthardt
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
| | - Megan N Aardema
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
| | - Gregory E Hall
- Chemistry Division, Brookhaven National Laboratory P.O. Box 5000 Upton, New York 11973-5000, USA
| | - Simon W North
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
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Warter ML, Gunthardt CE, Wei W, McBane GC, North SW. Nascent O 2 ( a 1Δ g, v = 0, 1) rotational distributions from the photodissociation of jet-cooled O 3 in the Hartley band. J Chem Phys 2018; 149:134309. [PMID: 30292221 DOI: 10.1063/1.5051540] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report rotational distributions for the O2 (a 1Δg) fragment from the photodissociation of jet-cooled O3 at 248, 266, and 282 nm. The rotational distributions show a population alternation that favors the even states, as previously reported for a 300 K sample by Valentini et al. [J. Chem. Phys. 86, 6745 (1987)]. The alternation from the jet-cooled precursor is much stronger than that observed by Valentini et al. and in contrast to their observations does not depend strongly on the O2 (a 1Δg) vibrational state or photolysis wavelength. The odd/even alternation diminishes substantially when the ozone beam temperature is increased from 60 to 200 K, confirming its dependence on parent internal energy. The magnitude of the even/odd alternation in product rotational states from the cold ozone sample, its temperature dependence, and other experimental and theoretical evidence reported since 1987 suggest that the alternation originates from a Λ-doublet propensity and not from a mass independent curve crossing effect, as previously proposed.
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Affiliation(s)
- Michelle L Warter
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
| | - Carolyn E Gunthardt
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
| | - Wei Wei
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
| | - George C McBane
- Department of Chemistry, Grand Valley State University, Allendale, Michigan 49401, USA
| | - Simon W North
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA
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Picconi D, Grebenshchikov SY. Signatures of a conical intersection in photofragment distributions and absorption spectra: photodissociation in the Hartley band of ozone. J Chem Phys 2014; 141:074311. [PMID: 25149790 DOI: 10.1063/1.4892919] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Photodissociation of ozone in the near UV is studied quantum mechanically in two excited electronic states coupled at a conical intersection located outside the Franck-Condon zone. The calculations, performed using recent ab initio PESs, provide an accurate description of the photodissociation dynamics across the Hartley/Huggins absorption bands. The observed photofragment distributions are reproduced in the two electronic dissociation channels. The room temperature absorption spectrum, constructed as a Boltzmann average of many absorption spectra of rotationally excited parent ozone, agrees with experiment in terms of widths and intensities of diffuse structures. The exit channel conical intersection contributes to the coherent broadening of the absorption spectrum and directly affects the product vibrational and translational distributions. The photon energy dependences of these distributions are strikingly different for fragments created along the adiabatic and the diabatic paths through the intersection. They can be used to reverse engineer the most probable geometry of the non-adiabatic transition. The angular distributions, quantified in terms of the anisotropy parameter β, are substantially different in the two channels due to a strong anticorrelation between β and the rotational angular momentum of the fragment O2.
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Affiliation(s)
- David Picconi
- Department of Chemistry, Technische Univeristät München, Lichtenbergstr. 4, 85747 Garching, Germany
| | - Sergy Yu Grebenshchikov
- Department of Chemistry, Technische Univeristät München, Lichtenbergstr. 4, 85747 Garching, Germany
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Ulrich CK, Chen J, Tokel O, Houston PL, Grebenshchikov SY. Photodissociation of ozone from 321 to 329 nm: the relative yields of O(3P2) with O2(X 3Σg(-)), O2(a 1Δg) and O2(b 1Σg(+)). J Phys Chem A 2013; 117:12011-9. [PMID: 23795961 DOI: 10.1021/jp4041088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Product imaging of O((3)P2) following dissociation of ozone has been used to determine the relative yields of the product channels O((3)P2) + O2(X (3)Σg(-)) of ozone. All three channels are prominent at all wavelengths investigated. O2 vibrational distributions for each channel and each wavelength are also estimated assuming Boltzmann rotational distributions. Averaged over wavelength in the measured range, the yields of the O((3)P2) + O2(X (3)Σg(-)), O((3)P2) + O2(a (1)Δg), and O((3)P2) + O2(b (1)Σg(+)) channels are 0.36, 0.31,and 0.34, respectively. Photofragment distributions in the spin-allowed channel O((3)P) + O2(X (3)Σg(-)) are compared with the results of quantum mechanical calculations on the vibronically coupled PESs of the singlet states B (optically bright) and R (repulsive). The experiments suggest that considerably more vibrational excitation and less rotational excitation occur than predicted by the quantum calculations. The rotational distributions, adjusted to fit the experimental images, suggest that the dissociation takes place from a more linear configuration than the Franck-Condon bending angle of 117°. The dissociation at most wavelengths results in a positive value of the anisotropy parameter, β, both in the experiment and in the calculations. Calculations indicate that both nonadiabatic transitions and intersystem crossings substantially reduce β below the nominal value of 2.
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Affiliation(s)
- C K Ulrich
- School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332, United States
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Brouard M, Hornung B, Aoiz FJ. Origin of collision-induced molecular orientation. PHYSICAL REVIEW LETTERS 2013; 111:183202. [PMID: 24237515 DOI: 10.1103/physrevlett.111.183202] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Indexed: 06/02/2023]
Abstract
Collision-induced rotational angular momentum orientation is a fundamental property of molecular scattering, which is sensitive to the balance between attractive and repulsive forces at play during collision. Here, we quantify a new mechanism leading to orientation, which is purely quantum mechanical in origin. Although the new mechanism is quite general, and will operate more widely in atomic and molecular scattering, it is observed here for impulsive hard shell collisions, for which the orientation vanishes classically. The quantum mechanism can thus be studied in isolation from other processes. The orientation is proposed to originate from the nonlocal nature of the quantum mechanical collision encounter.
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Affiliation(s)
- M Brouard
- The Department of Chemistry, The Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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Hancock G, Ritchie GA, Sharples TR. Vector correlations in the O 2(a 1Δ g, v = 1) fragment formed in the 265 nm photodissociation of ozone. Mol Phys 2013. [DOI: 10.1080/00268976.2013.780104] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- G. Hancock
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford, UK
| | - G. A.D. Ritchie
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory , Oxford, UK
| | - T. R. Sharples
- School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh, UK
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Ab initio quantum mechanical study of the O((1)D) formation in the photolysis of ozone between 300 and 330 nm. J Phys Chem A 2010; 114:9809-19. [PMID: 20509638 DOI: 10.1021/jp1028849] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Spin-allowed production of O((1)D) in the near-UV photolysis of ozone is studied using ab initio potential energy surfaces and quantum mechanics. The O((1)D) quantum yield, reconstructed from the absolute cross sections for eight initial vibrational states in the ground electronic state, is shown to agree with the measurements in a broad range of photolysis wavelengths and temperatures. Relative contributions of one- and two-quantum stretching and bending initial excitations are quantified, with the contribution of the antisymmetric stretch being dominant for lambda < 330 nm. Large scale structures in the low-resolution quantum yield are shown to reflect excitations in the high-frequency short bond stretch in the upper electronic state. Spin-forbidden contribution to the O((1)D) quantum yield at wavelengths lambda > 320 nm is estimated using ab initio energies of the triplet states and their spin-orbit couplings.
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Hancock G, Richmond G, Ritchie GA, Taylor S, Costen ML, Hall GE. Frequency modulated circular dichroism spectroscopy: application to ICN photolysis. Mol Phys 2010. [DOI: 10.1080/00268971003649323] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Horrocks SJ, Ritchie GAD, Sharples TR. Speed dependent rotational angular momentum polarization of the O2 (aΔg1) fragment following ozone photolysis in the wavelength range 248–265nm. J Chem Phys 2007; 127:114308. [PMID: 17887838 DOI: 10.1063/1.2775453] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The translational anisotropy and rotational angular momentum polarization of a selection of rotational states of the O2 (a 1Deltag; v=0) photofragment formed from ozone photolysis at 248, 260, and 265 nm have been determined using the technique of resonance enhanced multiphoton ionization in combination with time of flight mass spectrometry. At 248 nm, the dissociation is well described as impulsive in nature with all rotational states exhibiting similarly large, near-limiting values for the bipolar moments describing their angular momentum alignment and orientation. At 265 nm, however, the angular momentum polarization parameters determined for consecutive odd and even rotational states exhibit clear differences. Studies at the intermediate wavelength of 260 nm strongly suggest that such a difference in the angular momentum polarization is speed dependent and this proposal is consistent with the angular momentum polarization parameters extracted and reported previously for longer photolysis wavelengths [G. Hancock et al., Phys. Chem. Chem. Phys. 5, 5386 (2003); S. J. Horrocks et al., J. Chem. Phys. 126, 044308 (2007)]. The alternation of angular momentum polarization for successive odd and even J states may be a consequence of the different mechanisms leading to the formation of the two O2 (a 1Deltag) Lambda doublets. Specifically, the involvement of out of plane parent rotational motion is proposed as the origin for the observed depolarization for the Delta- relative to the Delta+ state.
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Affiliation(s)
- S J Horrocks
- Physical and Theoretical Chemistry Laboratory, The University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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