Spin dynamics and ortho–para conversion in H2O during the phase transition from gas to solid in external magnetic fields

Chemical Physics, vol. 612, pp. 113422

Abstract

The spin dynamics of water ice in the presence of external magnetic fields are investigated. The employed model is based on the approach introduced by Buntkowsky et al. (2008), which considers two nearest-neighbor water molecules and yields a four-spin system, as the abundant oxygen isotope has zero nuclear spin. The model is extended to include coupling to external magnetic fields, allowing us to analyze the interplay between magnetic dipole–dipole interactions and magnetic field coupling. Two types of configurations are examined: (i) static, homogeneous fields, corresponding to a time-independent interaction, and (ii) spatially varying sinusoidal fields in relative motion with the molecules, leading to a time-dependent interaction. All computations are performed within the density operator formalism. The ortho/para populations and the total spin projections are evaluated during the first tens of milliseconds following the gas-to-solid phase transition. For static homogeneous fields, we show that increasing field strength suppresses dipolar-induced depolarization. Assuming that all molecules are initially in the para state, we show that static homogeneous fields can drive the ortho population up to approximately 50%, whereas suitably chosen sinusoidal-field configurations can increase it beyond 90%. These results are relevant for schemes aiming to preserve or manipulate nuclear-spin polarization during deposition.

Authors 4

1. Chrysovalantis S. Kannis corresponding

   Heinrich Heine University Düsseldorf

   Affiliation as printed

   Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, Düsseldorf, 40225, NRW, Germany

2. R. Engels

   Forschungszentrum Jülich · GSI Helmholtz Centre for Heavy Ion Research

   Affiliation as printed

   GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, Darmstadt, 64291, Hessen, Germany

   Insitut für Kernphysik, Forschungszentrum Jülich, Wilhelm-Johnen-Straße 1, Jülich, 52428, NRW, Germany

3. Nicolas Faatz Aachen III. Physikalisches Institut B

   RWTH Aachen University · Forschungszentrum Jülich · GSI Helmholtz Centre for Heavy Ion Research

   Affiliation as printed

   GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, Darmstadt, 64291, Hessen, Germany

   III. Physikalisches Institut B, RWTH Aachen University, Otto-Blumenthal-Straße 19, Aachen, 52074, NRW, Germany

   Insitut für Kernphysik, Forschungszentrum Jülich, Wilhelm-Johnen-Straße 1, Jülich, 52428, NRW, Germany

4. M. Büscher

   Forschungszentrum Jülich · Heinrich Heine University Düsseldorf

   Affiliation as printed

   Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, Düsseldorf, 40225, NRW, Germany

   Peter-Grünberg Institut, Forschungszentrum Jülich, Wilhelm-Johnen-Straße 1, Jülich, 52428, NRW, Germany