title: Coherent evolution of parahydrogen induced polarisation using laser pump, NMR probe spectroscopy: Theoretical framework and experimental observation.
abstract: We recently reported a pump-probe method that uses a single laser pulse to introduce parahydrogen (p-H2) into a metal dihydride complex and then follows the time-evolution of the p-H2-derived nuclear spin states by NMR. We present here a theoretical framework to describe the oscillatory behaviour of the resultant hyperpolarised NMR signals using a product operator formalism. We consider the cases where the p-H2-derived protons form part of an AX, AXY, AXYZ or AA'XX' spin system in the product molecule. We use this framework to predict the patterns for 2D pump-probe NMR spectra, where the indirect dimension represents the evolution during the pump-probe delay and the positions of the cross-peaks depend on the difference in chemical shift of the p-H2-derived protons and the difference in their couplings to other nuclei. The evolution of the NMR signals of the p-H2-derived protons, as well as the transfer of hyperpolarisation to other NMR-active nuclei in the product, is described. The theoretical framework is tested experimentally for a set of ruthenium dihydride complexes representing the different spin systems. Theoretical predictions and experimental results agree to within experimental error for all features of the hyperpolarised1H and31P pump-probe NMR spectra. Thus we establish the laser pump, NMR probe approach as a robust way to directly observe and quantitatively analyse the coherent evolution of p-H2-derived spin order over micro-to-millisecond timescales.
authors.affiliation: Centre for Hyperpolarisation in Magnetic Resonance, Department of Chemistry, York Science Park, University of York, Heslington, York YO10 5NY, UK; Department of Chemistry, University of York, Heslington, York YO10 5DD, UK. Electronic address: meghan.halse@york.ac.uk.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Halse
authors.affiliation: Centre for Hyperpolarisation in Magnetic Resonance, Department of Chemistry, York Science Park, University of York, Heslington, York YO10 5NY, UK; Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
authors.forename: Barbara
authors.initials: B
authors.lastname: Procacci
authors.affiliation: Centre for Hyperpolarisation in Magnetic Resonance, Department of Chemistry, York Science Park, University of York, Heslington, York YO10 5NY, UK; Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
authors.forename: Sarah-Louise
authors.initials: SL
authors.lastname: Henshaw
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, UK. Electronic address: robin.perutz@york.ac.uk.
authors.forename: Robin N
authors.initials: RN
authors.lastname: Perutz
authors.affiliation: Centre for Hyperpolarisation in Magnetic Resonance, Department of Chemistry, York Science Park, University of York, Heslington, York YO10 5NY, UK; Department of Chemistry, University of York, Heslington, York YO10 5DD, UK. Electronic address: simon.duckett@york.ac.uk.
authors.forename: Simon B
authors.initials: SB
authors.lastname: Duckett
keywords: Hyperpolarisation; Long-lived states; Parahydrogen-induced polarisation; Photochemistry; Spin dynamics