Measurement of the 14N nuclear quadrupole resonance frequencies by the solid effect

Double resonance experiments in low magnetic field: Dynamic polarization of protons by 14N and measurement of low NQR frequencies

“…A dynamical increase of the proton magnetization above its equilibrium value can also be obtained using the solid effect [10]. This is the result of the ''forbidden" transitions at the frequency m Q ± m H , which occur simultaneously in both spin systems, and the spin-lattice relaxation of 14 N.…”

“…Next possibility of dynamically polarizing the proton spin system via the quadrupole 14 N spin system is given by the application of solid effect. As shown in [10] the dynamic polarization of protons may occur if in a weak magnetic field B we irradiate the sample by a strong rf magnetic field with the frequency m = m i ± m H , i = +, À, 0. When m = m i + m H , the magnetization of the dynamically polarized proton spin system points antiparallel to the direction of the magnetic field B.…”

“…When m = m i À m H , the proton magnetization points parallel to the direction of the magnetic field B. The population of the proton energy levels may again be described by the parameter z as given in Expressions (5) and (10) and the equilibrium value of z in case of no rf irradiation may be again denoted as z * , z * = hm H /2k B T. The ratio of the magnetization of the dynamically polarized proton spin system and the equilibrium proton magnetization at the Larmor frequency m H , z 0 /z * , is under the rf irradiation at the frequencies m = m i ± m H equal [10] …”

“…The sensitivity of the original NQDR technique [1] is in case of 14 N strongly reduced due to the spin quenching effect [2] when the asymmetry parameter g of the EFG tensor is nonzero. Several 1 H-14N NQDR techniques [3][4][5][6][7][8][9][10] have been developed to overcome this problem.…”

“…In the present paper we treat theoretically and experimentally three types of the 1 H- 14 (ii) Dynamic polarization of protons by 14 N using the solid effect [10] and (iii) A new NQDR technique based on the interaction between the quadrupole nuclei and protons at m H = m Q /2 and the rf irradiation the quadrupole nuclei with the rf magnetic field parallel to the static magnetic field. In this technique a two-quantum transitions in the proton spin system occurs simultaneously with a single-quantum transition in the quadrupole spin system conserving the total energy of the two spin systems.…”