UV, visible and near-IR spectroscopy methods based on CRDS have been used in the Bristol group for a number of important laboratory studies of atmospheric significance. These include a comprehensive investigation of the complicated photochemistry of formaldehyde, which is a key intermediate in atmospheric oxidation pathways, and an accurate determination of the Einstein A-coefficient for the near-IR absorption bands of O2 (via the nominally forbidden a1Δg – X3Σg– band excitation). This latter study included the first comprehensive test of CRDS against more established spectroscopic methods (in this case, FTIR spectroscopy) for quantitative determination of band intensities. The outcomes of the study provide the currently recommended values for line intensities of O2 in this spectral region in the HITRAN database, which is widely used by atmospheric scientists.
CRDS spectrum of the “forbidden” a – X transition of O2.
We have recently completed an extensive study of the photochemistry and quantum yields for NO2 production from photolysis of various organo nitrate compounds under tropospheric conditions. The outcomes are being incorporated into STOCHEM models to assess the impact of the formation of these organo nitrates on pathways for oxidation of volatile organic compounds in the atmosphere. The work is carried out in collaboration with Prof Dudley Shallcross, and with Prof Carl Percival of the University of Manchester.
CRDS is now being applied to determine the rates of reaction of Criegee intermediates which are generated in the atmospheric oxidation of alkenes by ozone. This project is a further collaboration with Prof Dudley Shallcross and Prof Carl Percival (Manchester), as well as Dr Craig Taatjes and colleagues at Sandia National Laboratory. This research is sponsored by the Natural Environment Research Council (NERC).
Representative publications:
A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy, R. Chhantyal Pun, A. Davey, D.E. Shallcross, C.J. Percival and A.J. Orr-Ewing, PCCP 17, 3617 – 3626 (2015).
NO2 quantum yields from ultraviolet photodissociation of methyl and isopropyl nitrate, P. Gorrotxategi Carbajo and A.J. Orr-Ewing, PCCP 12, 6084 – 6091 (2010).
Ultraviolet photolysis of HCHO: absolute HCO quantum yields by direct detection of the HCO photoproduct, P. Gorrotxategi Carbajo, S.C. Smith, A.L. Holloway, C.A. Smith, F.D. Pope, D.E. Shallcross and A.J. Orr-Ewing, J. Phys. Chem. A 112, 12437 – 12448 (2008).
Integrated absorption intensities and Einstein coefficients for the O2(a1Δg-X3Σg–) transition – a comparison of cavity ring-down and high-resolution Fourier transform spectroscopy using a long-path absorption cell, S.M. Newman, I.C. Lane, A.J. Orr-Ewing, D.M. Newnham and J. Ballard, J. Chem. Phys. 110, 10749 – 10757 (1999).
