Matthew Bain

All Publications

• High-Throughput Screening for Ultrafast Photochemical Reaction Discovery JOURNAL OF PHYSICAL CHEMISTRY LETTERS Bain, M., Castellanos, J., Bradforth, S. E. 2023; 14 (44): 9864-9871

  Abstract

  High-repetition-rate lasers present an opportunity to extend ultrafast spectroscopy from a detailed probe of singular model photochemical systems to a routine analysis technique in training machine learning models to aid the design cycle of photochemical syntheses. We bring together innovations in line scan cameras and micro-electro-mechanical grating modulators with sample delivery via high-pressure liquid chromatography pumps to demonstrate a transient absorption spectrometer that can characterize photoreactions initiated with ultrashort ultraviolet pulses in a time scale of minutes. Furthermore, we demonstrate that the ability to rapidly screen an important class of photochemical system, pyrimidine nucleosides, can be used to explore the effect of conformational modification on the evolution of excited-state processes.

  View details for DOI 10.1021/acs.jpclett.3c02389

  View details for Web of Science ID 001096767200001

  View details for PubMedID 37890453

• Nonadiabatic Coupling Effects in the 800 nm Strong-Field Ionization-Induced Coulomb Explosion of Methyl Iodide Revealed by Multimass Velocity Map Imaging and Ab <i>Initio</i> Simulation Studies JOURNAL OF PHYSICAL CHEMISTRY A Crane, S. W., Ge, L., Cooper, G. A., Carwithen, B. P., Bain, M., Smith, J. A., Hansen, C. S., Ashfold, M. R. 2021; 125 (44): 9594-9608

  Abstract

  The Coulomb explosion (CE) of jet-cooled CH3I molecules using ultrashort (40 fs), nonresonant 805 nm strong-field ionization at three peak intensities (260, 650, and 1300 TW cm-2) has been investigated by multimass velocity map imaging, revealing an array of discernible fragment ions, that is, Iq+ (q ≤ 6), CHn+ (n = 0-3), CHn2+ (n = 0, 2), C3+, H+, H2+, and H3+. Complementary ab initio trajectory calculations of the CE of CH3IZ+ cations with Z ≤ 14 identify a range of behaviors. The CE of parent cations with Z = 2 and 3 can be well-described using a diatomic-like representation (as found previously) but the CE dynamics of all higher CH3IZ+ cations require a multidimensional description. The ab initio predicted Iq+ (q ≥ 3) fragment ion velocities are all at the high end of the velocity distributions measured for the corresponding Iq+ products. These mismatches are proposed as providing some of the clearest insights yet into the roles of nonadiabatic effects (and intramolecular charge transfer) in the CE of highly charged molecular cations.

  View details for DOI 10.1021/acs.jpca.1c06346

  View details for Web of Science ID 000720777300004

  View details for PubMedID 34709807

• Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Cox, J. M., Bain, M., Kellogg, M., Bradforth, S. E., Lopez, S. A. 2021; 143 (18): 7002-7012

  Abstract

  Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly strained, Dewar-type bicyclohexenes. While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the so-called "perfluoro effect", the resulting electronic structure and photochemical reactivity of hexafluorobenzene is still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4π-electrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ∼100 nm Stokes shift in fluorescence-in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway toward hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.

  View details for DOI 10.1021/jacs.1c01506

  View details for Web of Science ID 000651748000031

  View details for PubMedID 33938749

• Ultraviolet photochemistry of ethane: implications for the atmospheric chemistry of the gas giants CHEMICAL SCIENCE Chang, Y., Yang, J., Chen, Z., Zhang, Z., Yu, Y., Li, Q., He, Z., Zhang, W., Wu, G., Ingle, R. A., Bain, M., Ashfold, M. R., Yuan, K., Yang, X., Hansen, C. S. 2020; 11 (19): 5089-5097

  Abstract

  Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH2, CH3 and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini-Huygens fly-by of Jupiter.

  View details for DOI 10.1039/d0sc01746a

  View details for Web of Science ID 000536688300025

  View details for PubMedID 34122966

  View details for PubMedCentralID PMC8159213

• Quantifying rival bond fission probabilities following photoexcitation: C-S bond fission in <i>t</i>-butylmethylsulfide CHEMICAL SCIENCE Bain, M., Hansen, C. S., Karsili, T. N., Ashfold, M. R. 2019; 10 (20): 5290-5298

  Abstract

  We illustrate a new, collision-free experimental strategy that allows determination of the absolute probabilities of rival bond fission processes in a photoexcited molecule - here t-butylmethylsulfide (BSM). The method combines single photon ('universal') ionization laser probe methods, simultaneous imaging of all probed fragments (multi-mass ion imaging) and the use of an appropriate internal calibrant (here dimethylsulfide). Image analysis allows quantification of the dynamics of the rival B-SM and BS-M bond fission processes following ultraviolet (UV) excitation of BSM and shows the former to be twice as probable, despite the only modest (∼2%) differences in the respective ground state equilibrium C-S bond lengths or bond strengths. Rationalising this finding should provide a stringent test of the two close-lying, coupled excited states of 1A'' symmetry accessed by UV excitation in BSM and related thioethers, of the respective transition dipole moment surfaces, and of the geometry dependent non-adiabatic couplings that enable the rival C-S bond fissions.

  View details for DOI 10.1039/c9sc00738e

  View details for Web of Science ID 000468791800009

  View details for PubMedID 31191885

  View details for PubMedCentralID PMC6540878

• Exploring the Dynamics of the Photoinduced Ring-Opening of Heterocyclic Molecules JOURNAL OF PHYSICAL CHEMISTRY LETTERS Ashfold, M. R., Bain, M., Hansen, C. S., Ingle, R. A., Karsili, T. V., Marchetti, B., Murdock, D. 2017; 8 (14): 3440-3451

  Abstract

  Excited states formed by electron promotion to an antibonding σ* orbital are now recognized as key to understanding the photofragmentation dynamics of a broad range of heteroatom containing small molecules: alcohols, thiols, amines, and many of their aromatic analogues. Such excited states may be populated by direct photoexcitation, or indirectly by nonadiabatic transfer of population from some other optically excited state (e.g., a ππ* state). This Perspective explores the extent to which the fast-growing literature pertaining to such (n/π)σ*-state mediated bond fissions can inform and enhance our mechanistic understanding of photoinduced ring-opening in heterocyclic molecules.

  View details for DOI 10.1021/acs.jpclett.7b01219

  View details for Web of Science ID 000406358000044

  View details for PubMedID 28661140

• Ultraviolet photochemistry of 2-bromothiophene explored using universal ionization detection and multi-mass velocity-map imaging with a PImMS2 sensor JOURNAL OF CHEMICAL PHYSICS Ingle, R. A., Hansen, C. S., Elsdon, E., Bain, M., King, S. J., Lee, J. L., Brouard, M., Vallance, C., Turchetta, R., Ashfold, M. R. 2017; 147 (1): 013914

  Abstract

  The ultraviolet photochemistry of 2-bromothiophene (C4H3SBr) has been studied across the wavelength range 265-245 nm using a velocity-map imaging (VMI) apparatus recently modified for multi-mass imaging and vacuum ultraviolet (VUV, 118.2 nm) universal ionization. At all wavelengths, molecular products arising from the loss of atomic bromine were found to exhibit recoil velocities and anisotropies consistent with those reported elsewhere for the Br fragment [J. Chem. Phys. 142, 224303 (2015)]. Comparison between the momentum distributions of the Br and C4H3S fragments suggests that bromine is formed primarily in its ground (2P3/2) spin-orbit state. These distributions match well at high momentum, but relatively fewer slow moving molecular fragments were detected. This is explained by the observation of a second substantial ionic product, C3H3+. Analysis of ion images recorded simultaneously for several ion masses and the results of high-level ab initio calculations suggest that this fragment ion arises from dissociative ionization (by the VUV probe laser) of the most internally excited C4H3S fragments. This study provides an excellent benchmark for the recently modified VMI instrumentation and offers a powerful demonstration of the emerging field of multi-mass VMI using event-triggered, high frame-rate sensors, and universal ionization.

  View details for DOI 10.1063/1.4979559

  View details for Web of Science ID 000405089400015

  View details for PubMedID 28688387