Many-spin quantum dynamics during cross polarization in 8CB

CHATTAH, ANA KARINA; ÁLVAREZ, GONZALO A.; LEVSTEIN, PATRICIA R.; CUCCHIETTI, FERNANDO M.; PASTAWSKI, HORACIO M.; RAYA, JÉSUS; HIRSCHINGER, JÉRÔME

American Institute of Physics

Lugar: MELVILLE, NY 11747-4501 USA; Año: 2003 vol. 119 p. 7943 - 7943

font size="2"> We analyze theoretically and experimentally the quantum dynamics of a three-spin-1/2 system during cross polarization (CP). Our analysis takes into account a Hamiltonian behavior for a carbon C-13 coupled to two protons H-1 while the coupling to a spin bath is treated in the fast fluctuation approximation. This model is applied to the methylene and biphenyl groups of the smectic and nematic phases of the liquid crystal 4-n-octyl-4(´)-cyanobiphenyl (8CB). Experimental data from standard CP, combined with our theoretical results, allow us to separate the homonuclear H-1-H-1 and heteronuclear H-1-C-13 residual dipolar couplings. These values are in good agreement with those obtained by using a combination of CP under Lee-Goldburg conditions and standard CP data. A well differentiated relaxation behavior among the two phases seems to indicate that while the extreme narrowing approximation is appropriate for the nematic phase, the description of the smectic phase require