title: Evidence for Coherent Transfer of para-Hydrogen-Induced Polarization at Low Magnetic Fields.
abstract: We have investigated the mechanism of para-hydrogen-induced polarization (PHIP) transfer from the original strongly aligned protons to other nuclei at low external magnetic fields. Although it is known that PHIP is efficiently transferred at low fields, the nature of the transfer mechanism, that is, coherent spin mixing or cross-relaxation, is not well established. Polarization transfer kinetics for individual protons of styrene was, for the first time, measured and modeled theoretically. Pronounced oscillations were observed indicating a coherent transfer mechanism. Spin coherences were excited by passing through an avoided level crossing of the nuclear spin energy levels. Transfer at avoided level crossings is selective with respect to spin order. Our work provides evidence that the coherent PHIP transfer mechanism is dominant at low magnetic fields.
authors.affiliation: International Tomography Center SB RAS , Novosibirsk 630090, Russia.|Novosibirsk State University , Novosibirsk 630090, Russia.
authors.forename: Alexey S
authors.initials: AS
authors.lastname: Kiryutin
authors.affiliation: International Tomography Center SB RAS , Novosibirsk 630090, Russia.|Novosibirsk State University , Novosibirsk 630090, Russia.
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Yurkovskaya
authors.affiliation: Novosibirsk State University , Novosibirsk 630090, Russia.|Utrecht University , NL-3584 CH Utrecht, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Kaptein
authors.affiliation: Freie Universität Berlin , Berlin D-14195, Germany.
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Vieth
authors.affiliation: International Tomography Center SB RAS , Novosibirsk 630090, Russia.|Novosibirsk State University , Novosibirsk 630090, Russia.
authors.forename: Konstantin L
authors.initials: KL
authors.lastname: Ivanov
keywords: PHIP; level anticrossings; polarization transfer; spin coherences; spin hyperpolarization