title: ESR lineshape and 1H spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals--joint analysis.
abstract: Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d16 containing (15)N and (14)N isotopes. The NMRD experiments refer to (1)H spin-lattice relaxation measurements in a broad frequency range (10 kHz-20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recently presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the (1)H relaxation of the solvent. The (1)H relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin-nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.
authors.affiliation: University of Warmia & Mazury in Olsztyn, Faculty of Mathematics & Computer Science, Sloneczna 54, PL-10710 Olsztyn, Poland.
authors.forename: D
authors.initials: D
authors.lastname: Kruk
authors.affiliation: Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland.
authors.forename: S K
authors.initials: SK
authors.lastname: Hoffmann
authors.affiliation: Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Goslar
authors.affiliation: Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland.
authors.forename: S
authors.initials: S
authors.lastname: Lijewski
authors.affiliation: Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Kubica-Misztal
authors.affiliation: Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Korpała
authors.affiliation: Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland.
authors.forename: I
authors.initials: I
authors.lastname: Oglodek
authors.affiliation: Arrhenius Laboratory, Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Kowalewski
authors.affiliation: Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth, Germany.
authors.forename: E A
authors.initials: EA
authors.lastname: Rössler
authors.affiliation: Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Moscicki