title: Enhancement of quantum rotor NMR signals by frequency-selective pulses.
abstract: Quantum-rotor-induced polarisation (QRIP) enhancement is exhibited by substances which contain freely rotating methyl groups in the solid state, provided that the methyl groups contain a (13)C nucleus. Strong signal enhancements are observed in solution NMR when the material is first equilibrated at cryogenic temperatures, then rapidly dissolved with a warm solvent and transferred into an NMR magnet. QRIP leads to strongly-enhanced (13)C NMR signals, but relatively weak enhancements of the (1)H signals. We show that the (1)H signals suffer from a partial cancellation of degenerate contributions, which may be corrected by applying a frequency-selective π pulse to the inner peaks of the (13)C multiplet prior to (1)H observation.
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Soumya Singha
authors.initials: SS
authors.lastname: Roy
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom; Institut de Chimie des Substances Naturelles, CNRS UPR2301, Avenue de la Terrasse, 91190 Gif-sur-Yvette, France.
authors.forename: Jean-Nicolas
authors.initials: JN
authors.lastname: Dumez
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Stevanato
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Benno
authors.initials: B
authors.lastname: Meier
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hill-Cousins
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Richard C D
authors.initials: RCD
authors.lastname: Brown
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pileio
authors.affiliation: School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom. Electronic address: mhl@soton.ac.uk.
authors.forename: Malcolm H
authors.initials: MH
authors.lastname: Levitt
keywords: Hyperpolarisation; Long-lived states; Methyl groups; QRIP; Quantum-rotor-induced polarisation; Tunneling