Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Photophysical oxidation of HCHO produces HO2 radicals

Nature Chemistry volume 15, pages 1350–1357 (2023)Cite this article

Subjects

Abstract

Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330 nm and photolyses to form H and HCO radicals, which then react with O2 to form HO2. Here we show HCHO has an additional HO2 formation pathway. At photolysis energies below the energetic threshold for radical formation we directly detect HO2 at low pressures by cavity ring-down spectroscopy and indirectly detect HO2 at 1 bar by Fourier-transform infrared spectroscopy end-product analysis. Supported by electronic structure theory and master equation simulations, we attribute this HO2 to photophysical oxidation (PPO): photoexcited HCHO relaxes non-radiatively to the ground electronic state where the far-from-equilibrium, vibrationally activated HCHO molecules react with thermal O2. PPO is likely to be a general mechanism in tropospheric chemistry and, unlike photolysis, PPO will increase with increasing O2 pressure.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Formaldehyde energy-level diagram showing accessible PCO and PPO pathways following excitation to the indicated S1 levels.
Fig. 2: Action spectrum of HCHO measured by CRDS of the HO2 radical.
Fig. 3: The pressure dependence of HO2 formation.
Fig. 4: FTIR spectra of reaction end products following excitation of 1 torr HCHO to the 2141 level in different buffer gases, as indicated.
Fig. 5: Energy dependence of rate coefficients and quantum yields.

Similar content being viewed by others

Data availability

All data are available in the paper or the supplementary materials. Source data are available for Figs. 2, 3, 4 and 5. Source data are provided with this paper.

References

  1. Finlayson-Pitts, B. J. & Pitts, J. N. Jr Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications (Academic Press, 2000).

  2. Atkinson, R. & Arey, J. Atmospheric degradation of volatile organic compounds. Chem. Rev. 103, 4605–4638 (2003).

    Article  CAS  PubMed  Google Scholar 

  3. Glowacki, D. R. et al. Interception of excited vibrational quantum states by O2 in atmospheric association reactions. Science 337, 1066–1069 (2012).

    Article  CAS  PubMed  Google Scholar 

  4. Vaida, V. & Donaldson, D. J. Red-light initiated atmospheric reactions of vibrationally excited molecules. Phys. Chem. Chem. Phys. 16, 827–836 (2014).

    Article  CAS  PubMed  Google Scholar 

  5. Tully, J. C. Reactions of O(1D) with atmospheric molecules. J. Chem. Phys. 62, 1893–1898 (1975).

    Article  CAS  Google Scholar 

  6. Ruscic B. & Bross, D. H. Active Thermochemical Tables v. 1.124 (Argonne National Laboratory, accessed 20 December 2022); https://atct.anl.gov/

  7. Houston, P. L. & Moore, C. B. Formaldehyde photochemistry: appearance rate, vibrational relaxation, and energy distribution of the CO product. J. Chem. Phys. 65, 757–770 (1976).

    Article  CAS  Google Scholar 

  8. Chuang, M.-C., Foltz, M. F. & Moore, C. B. T1 barrier height, S1–T1 intersystem crossing rate, and S0 radical dissociation threshold for HCHO, D2CO, and HDCO. J. Chem. Phys. 87, 3855–3864 (1987).

    Article  CAS  Google Scholar 

  9. Valachovic, L. R. et al. Photoinitiated HCHO unimolecular decomposition: accessing H + HCO products via S0 and T1 pathways. J. Chem. Phys. 112, 2752–2761 (2000).

    Article  CAS  Google Scholar 

  10. Townsend, D. et al. The roaming atom: straying from the reaction path in formaldehyde decomposition. Science 306, 1158–1161 (2004).

    Article  CAS  PubMed  Google Scholar 

  11. Troe, J. Analysis of quantum yields for the photolysis of formaldehyde at λ > 310 nm. J. Phys. Chem. A 111, 3868–3874 (2007).

    Article  CAS  PubMed  Google Scholar 

  12. Quinn, M. S. et al. Rotational resonances in the HCHO roaming reaction are revealed by detailed correlations. Science 369, 1592–1596 (2020).

    Article  CAS  PubMed  Google Scholar 

  13. Quinn, M. S., Andrews, D. U., Nauta, K., Jordan, M. J. T. & Kable, S. H. The energy dependence of CO(v,J) produced from via the transition state, roaming, and triple fragmentation channels. J. Chem. Phys. 147, 013935 (2017).

    Article  PubMed  Google Scholar 

  14. Feller, D., Dupuis, M. & Garrett, B. C. Barrier for the HCHO → H2 + CO reaction: a discrepancy between high-level electronic structure calculations and experiment. J. Chem. Phys. 113, 218–226 (2000).

    Article  CAS  Google Scholar 

  15. Bauerfeldt, G. F., de Albuquerque, L. M. M., Arbilla, G. & da Silva, E. C. Unimolecular reactions on formaldehyde S0 PES. J. Molec. Struct. (Theochem) 580, 147–160 (2002).

    Article  CAS  Google Scholar 

  16. Zhang, X., Rheinecker, J. L. & Bowman, J. M. Quasiclassical trajectory study of formaldehyde unimolecular dissociation: HCHO → H2 + CO, H + HCO. J. Chem. Phys. 122, 114313 (2005).

    Article  PubMed  Google Scholar 

  17. Harding, L. B., Klippenstein, S. J. & Jasper, A. W. Ab initio methods for reactive potential surfaces. Phys. Chem. Chem. Phys. 9, 4055–4070 (2007).

    Article  CAS  PubMed  Google Scholar 

  18. Clark, J. H., Moore, C. B. & Nogar, N. S. The photochemistry of formaldehyde: absolute quantum yields, radical reactions, and NO reactions. J. Chem. Phys. 68, 1264–1271 (1978).

    Article  CAS  Google Scholar 

  19. Horowitz, A. & Calvert, J. G. Wavelength dependence of the quantum efficiencies of the primary processes in formaldehyde photolysis at 25 °C. Int. J. Chem. Kin. 10, 805–819 (1978).

    Article  CAS  Google Scholar 

  20. Moortgat, G. K., Šlemr, F., Seiler, W. & Warneck, P. Relative quantum yields of H2 and CO in the wavelength range 70–360 nm. Chem. Phys. Lett. 54, 444–447 (1978).

    Article  CAS  Google Scholar 

  21. Moortgat, G. K. & Warneck, P. CO and H2 quantum yields in the photodecomposition of formaldehyde in air. J. Chem. Phys. 70, 3639–3651 (1979).

    Article  CAS  Google Scholar 

  22. Moortgat, G. K., Seiler, W. & Warneck, P. Photodissociation of HCHO in air: CO and H2 quantum yields at 220 and 300 K. J. Chem. Phys. 78, 1185–1190 (1983).

    Article  CAS  Google Scholar 

  23. Smith, G. D., Molina, L. T. & Molina, M. J. Measurement of radical quantum yields from formaldehyde photolysis between 269 and 339 nm. J. Phys. Chem. A 106, 1233–1240 (2002).

    Article  CAS  Google Scholar 

  24. Atkinson, R. et al Evaluated kinetic and photochemical data for atmospheric chemistry: volume II gas phase reactions of organic species. Atmos. Chem. Phys. 6, 3625–4055 (2006); http://iupac.pole-ether.fr. Datasheet updated: 16 April 2013; last change in preferred values: 16 April 2013.

  25. Campbell, J. S., Nauta, K., Hansen, C. S. & Kable, S. H. POPTARTS: a new method to determine quantum yields in a molecular beam. J. Phys. Chem. A 126, 9268–9275 (2022).

    Article  CAS  PubMed  Google Scholar 

  26. Su, F., Calvert, J. G. & Shaw, J. H. Mechanism of the photooxidation of gaseous formaldehyde. J. Phys. Chem. 83, 3185–3191 (1979).

    Article  CAS  Google Scholar 

  27. Terentis, A. C., Waugh, S. E., Metha, G. F. & Kable, S. H. HCO (N, Ka, Kc, J) distributions from near-threshold photolysis of HCHO (J, Ka, Kc). J. Chem. Phys. 108, 3187–3198 (1998).

    Article  CAS  Google Scholar 

  28. Assaf, E., Liu, L., Schoemaecker, C. & Fittschen, C. Absorption spectrum and absorption cross sections of the 2ν1 band of HO2 between 20 and 760 torr air in the range 6636 and 6639 cm−1. J. Quant. Spectrosc. Radiat. Transf. 211, 107–114 (2018).

    Article  CAS  Google Scholar 

  29. Shaw, M. F. et al. Photo-tautomerization of acetaldehyde as a photochemical source of formic acid in the troposphere. Nat. Commun. 9, 2584 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  30. Clouthier, D. J. & Ramsay, D. A. The spectroscopy of formaldehyde and thioformaldehyde. Annu. Rev. Phys. Chem. 34, 31–58 (1983).

    Article  CAS  Google Scholar 

  31. Motsch, M. et al. Spectroscopy of the A1A2–X1A1 transition of formaldehyde in the 30140–30790 cm–1 range: the 210430 and 220410 rovibrational bands. J. Molec. Spectrosc. 252, 25–30 (2008).

    Article  CAS  Google Scholar 

  32. Jenkin, M. E., Hurley, M. D. & Wallington, T. J. Investigation of the radical product channel of the CH3C(O)O2 + HO2 reaction in the gas phase. Phys. Chem. Chem. Phys. 9, 3149–3162 (2007).

    Article  CAS  PubMed  Google Scholar 

  33. Morajkar, P., Schoemaecker, C., Okumura, M. & Fittschen, C. Direct measurement of the equilibrium constants of the reaction of formaldehyde and acetaldehyde with HO2 radicals. Int. J. Chem. Kinet. 46, 245–259 (2014).

    Article  CAS  Google Scholar 

  34. Bixon, M. & Jortner, J. Intramolecular radiationless transitions. J. Chem. Phys. 48, 715–726 (1968).

    Article  CAS  Google Scholar 

  35. Weisshaar, J. C. & Moore, C. B. Isotope, electric field, and vibrational state dependence of single rotational level lifetimes of S1 formaldehyde. J. Chem. Phys. 72, 5415–5425 (1980).

    Article  CAS  Google Scholar 

  36. Yin, H. M., Kable, S. H. X. & Bowman, J. M. Signatures of HCHO photodissociation from two electronic states. Science 311, 1443–1446 (2006).

    Article  CAS  PubMed  Google Scholar 

  37. Miller, R. G. & Lee, E. K. C. Single vibronic level photochemistry of formaldehydes in the à 1A2 state: radiative and nonradiative processes in HCHO, HDCO, and D2CO. J. Chem. Phys. 68, 4448–4464 (1978).

    Article  CAS  Google Scholar 

  38. Huynh, L. K., Tirtowidjojo, M. & Truong, T. N. Theoretical study on kinetics of the HCHO + O2 → HCO + HO2 reaction. Chem. Phys. Lett. 469, 81–84 (2009).

    Article  CAS  Google Scholar 

  39. Michael, J. V., Kumaran, S. S. & Su, M.-C. Rate constants for CH3 + O2 → CH3O + O at high temperature and evidence for HCHO + O2 → HCO + HO2. J. Phys. Chem. A 103, 5942–5948 (1999).

    Article  CAS  Google Scholar 

  40. Vasudevan, V., Davidson, D. F., Hanson, R. K., Bowman, C. T. & Golden, D. M. High-temperature measurements of the rates of the reactions CH2O + Ar → products and CH2O + O2 → products. Proc. Combust. Inst. 31, 175–183 (2007).

    Article  Google Scholar 

  41. Hidaka, Y. et al. Shock-tube study of CH2O pyrolysis and oxidation. Combust. Flame 92, 365–376 (1993).

    Article  CAS  Google Scholar 

  42. Eiteneer, B., Yu, C.-L., Goldenberg, M. & Frenklach, M. Determination of rate coefficients for reactions of formaldehyde pyrolysis and oxidation in the gas phase. J. Phys. Chem. A 102, 5196–5205 (1998).

    Article  CAS  Google Scholar 

  43. Srinivasan, N. K., Su, M.-C., Sutherland, J. W. & Michael, J. V. Reflected shock tube studies of high-temperature rate constants for CH3 + O2, HCHO + O2, and OH + O2. J. Phys. Chem. A 109, 7902–7914 (2005).

    Article  CAS  PubMed  Google Scholar 

  44. Maranzana, A., Barker, J. R. & Tonachini, G. Master equation simulations of competing unimolecular and bimolecular reactions: application to OH production in the reaction of acetyl radical with O2. Phys. Chem. Chem. Phys. 9, 4129–4141 (2007).

    Article  CAS  PubMed  Google Scholar 

  45. Barker, J. R., et al. MultiWell-2022 Software Suite (University of Michigan, 2022); http://clasp-research.engin.umich.edu/multiwell/

  46. Barker, J. R. Multiple-well, multiple-path unimolecular reaction systems. I. MultiWell computer program suite. Int. J. Chem. Kinet. 33, 232–245 (2001).

    Article  CAS  Google Scholar 

  47. Barker, J. R. Energy transfer in master equation simulations: a new approach. Int. J. Chem. Kinet. 41, 748–763 (2009).

    Article  CAS  Google Scholar 

  48. Zhang, X., Zou, S., Harding, L. B. & Bowman, J. M. A global ab Initio potential energy surface for formaldehyde. J. Phys. Chem. A. 108, 8980–8986 (2004).

    Article  CAS  Google Scholar 

  49. Maeda, S., Ohno, K. & Morokuma, K. Automated global mapping of minimal energy points on seams of crossing by the anharmonic downward distortion following method: a case study of H2CO. J. Phys. Chem. A 113, 1704–1710 (2009).

    Article  CAS  PubMed  Google Scholar 

  50. Lahankar, S. A., Chambreau, S. D., Zhang, X., Bowman, J. M. & Suits, A. G. Energy dependence of the roaming atom pathway in formaldehyde decomposition. J. Chem. Phys. 126, 044314 (2007).

    Article  PubMed  Google Scholar 

  51. Morajkar, P., Bossolasco, A., Schoemaecker, C. & Fittschen, C. Photolysis of CH3CHO at 248 nm: evidence of triple fragmentation from primary quantum yield of CH3 and HCO radicals and H atoms. J. Chem. Phys. 140, 214308 (2014).

    Article  PubMed  Google Scholar 

  52. Stone, D., Whalley, L. K. & Heard, D. E. Tropospheric OH and HO2 radicals: field measurements and model comparisons. Chem. Soc. Rev. 41, 6348–6404 (2012).

    Article  CAS  PubMed  Google Scholar 

  53. Staak, M., Gash, E. W., Venables, D. S. & Ruth, A. A. The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm–1. J. Mol. Spectrosc. 229, 115–121 (2005).

    Article  CAS  Google Scholar 

  54. Ruth, A. A., Heitmann, U., Heinecke, E. & Fittschen, C. The rotationally resolved absorption spectrum of formaldehyde from 6547 to 7051 cm–1. Z. Phys. Chem. 229, 1609–1624 (2015).

    Article  CAS  Google Scholar 

  55. Western, C. M. PGOPHER, a program for simulating rotational, vibrational and electronic spectra. J. Quant. Spectrosc Radiat. Transfer 186, 221–242 (2017).

    Article  CAS  Google Scholar 

  56. Frisch, M. J. et al. Gaussian 16, revision C.01 (Gaussian, Inc., 2016).

  57. Truhlar, D. G., Steckler, R. & Gordon, M. S. Potential energy surfaces for polyatomic reaction dynamics. Chem. Rev. 87, 217–236 (1987).

    Article  CAS  Google Scholar 

  58. Durant, J. L. Evaluation of transition state properties by density functional theory. Chem. Phys. Lett. 256, 595–602 (1996).

    Article  CAS  Google Scholar 

  59. Shaw, M. F. Photochemical Formation of Enols from Carbonyls. PhD thesis, The Univ. Sydney (2017).

  60. Rowell, K. N., Kable, S. H. & Jordan, M. J. T. Structural effects on the Norrish type I α‐bond cleavage of tropospherically important carbonyls. J. Phys. Chem. A 123, 10381–10396 (2019).

    Article  CAS  PubMed  Google Scholar 

  61. Rowell, K. N., Kable, S. H. & Jordan, M. J. T. An assessment of the tropospherically accessible photo-initiated ground state chemistry of organic carbonyls. Atmos. Chem. Phys. 2022, 929–949 (2022).

    Article  Google Scholar 

  62. Johnson, R. D. III (ed.) NIST Computational Chemistry Comparison and Benchmark Database, NIST Standard Reference Database Number 101 Release 21, August 2020 (CCCBDB, accessed 1 march 2021); http://cccbdb.nist.gov/

  63. Lubic, K. G., Amano, T., Uehara, H., Kawaguchi, K. & Hirota, E. The ν1 band of the DO2 radical by difference frequency laser and diode laser spectroscopy: the equilibrium structure of the hydroperoxyl radical. J. Chem. Phys. 81, 4826–4831 (1984).

    Article  CAS  Google Scholar 

  64. Herzberg, G. Electronic Spectra and Electronic Structure of Polyatomic Molecules (Van Nostrand Reinhold, 1966).

  65. Huber K. P. & Herzberg, G. Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, 1979).

  66. Duncan, J. L. The ground-state average and equilibrium structures of formaldehyde and ethylene. Mol. Phys. 28, 1177–1191 (1974).

    Article  CAS  Google Scholar 

  67. Laury, M. L. et al. Harmonic vibrational frequencies: scale factors for pure, hybrid, hybrid meta, and double-hybrid functionals in conjunction with correlation consistent basis sets. J. Comp. Chem. 32, 2339–2347 (2011).

    Article  CAS  Google Scholar 

  68. Kesharwani, M. K., Brauer, B. & Martin, J. M. L. Frequency and zero-point vibrational energy scale factors for double-hybrid density functionals (and other selected methods): can anharmonic force fields be avoided? J. Phys. Chem. A 119, 1701–1714 (2015).

    Article  CAS  PubMed  Google Scholar 

  69. Tardy, D. C. & Rabinovitch, B. S. Intermolecular vibrational energy transfer in thermal unimolecular systems. Chem. Rev. 77, 369–408 (1977).

    Article  CAS  Google Scholar 

  70. Weaver, A. B. & Alexeenko, A. A. Revised variable soft sphere and Lennard–Jones model parameters for eight common gases up to 2200 K. J. Phys. Chem. Ref. Data 44, 023103 (2015).

    Article  Google Scholar 

  71. Troe, J. Theory of thermal unimolecular reactions at low pressures. I. Solutions of the master equation. J. Chem. Phys. 66, 4745–4757 (1977).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We thank C. Hecquet and C. Schoemaecker for assistance with the Lille photolysis laser. B.A.W. and M.E.C. acknowledge Australian Government Research Training Scheme scholarships. Funding: Australian Research Council grant DP190102013 (B.A.W., M.E.C., P.S., K.N., M.J.T.J., S.H.K.); French ANR agency under contract number ANR-11-Labx-0005-01 CaPPA (Chemical and Physical Properties of the Atmosphere) (E.A., C.F.); Région Hauts-de-France, the Ministère de l’Enseignement Supérieur et de la Recherche (CPER Climibio) (E.A., C.F.); European Fund for Regional Economic Development (E.A., C.F.). Computation was supported with the assistance of resources from the National Computational Infrastructure (NCI Australia), an NCRIS-enabled capability supported by the Australian Government (M.E.C., M.J.T.J.).

Author information

Author notes

  1. Blair A. Welsh

    Present address: Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA

  2. Emmanuel Assaf

    Present address: Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA

  3. Emmanuel Assaf

    Present address: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA

  4. Paolo Sebastianelli

    Present address: School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, New South Wales, Australia

Authors and Affiliations

  1. School of Chemistry, University of New South Wales, Kensington, New South Wales, Australia

    Blair A. Welsh, Klaas Nauta, Paolo Sebastianelli & Scott H. Kable

  2. School of Chemistry, University of Sydney, Sydney, New South Wales, Australia

    Maggie E. Corrigan & Meredith J. T. Jordan

  3. Université Lille, CNRS, UMR 8522, PC2A—Physicochimie des Processus de Combustion et de l’Atmosphère, Lille, France

    Emmanuel Assaf & Christa Fittschen

Authors
  1. Blair A. Welsh
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Maggie E. Corrigan
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Emmanuel Assaf
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Klaas Nauta
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Paolo Sebastianelli
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Meredith J. T. Jordan
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Christa Fittschen
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Scott H. Kable
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

Conceptualization: M.J.T.J. and S.H.K. Methodology and investigation: B.A.W., M.E.C., E.A., K.N., P.S., M.J.T.J., C.F. and S.H.K. Funding acquisition and project administration: M.J.T.J., C.F. and S.H.K. Supervision: K.N., M.J.T.J., C.F. and S.H.K. Writing—original draft: M.J.T.J. and S.H.K. Writing—review and editing: B.A.W., M.E.C., E.A., K.N., P.S., M.J.T.J., C.F. and S.H.K.

Corresponding authors

Correspondence to Meredith J. T. Jordan or Scott H. Kable.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Chemistry thanks A. R. Ravishankara, Paul Seakins and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Methods and discussion, Figs. 1–12 and Tables 1–8.

Source data

Source Data Fig. 2

CRDS spectrum and simulation data.

Source Data Fig. 3

CRDS spectrum and master equation modelling data.

Source Data Fig. 4

FTIR spectrum data.

Source Data Fig. 5

Rate coefficient, CRDS and master equation modelling data.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Welsh, B.A., Corrigan, M.E., Assaf, E. et al. Photophysical oxidation of HCHO produces HO2 radicals. Nat. Chem. 15, 1350–1357 (2023). https://doi.org/10.1038/s41557-023-01272-4

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41557-023-01272-4

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing