Multiphoton NMR spectroscopy on a spin system with I=1/2

Abstract

Articles you may be interested inOn the theory of double quantum NMR in polymer systems: The second cumulant approximation for many spin I = 1/2 systems J. Chem. Phys. 139, 194905 (2013); 10.1063/1.4830410 Determination of spin Hamiltonians from projected single reference configuration interaction calculations. I. Spin 1/2 systems J. Chem. Phys. 133, 044106 (2010); 10.1063/1.3458642Electron spin echo envelope modulation spectroscopy on orientationally disordered systems: Line shape singularities in S=1/2, I=1/2 spin systems J. Chem. Phys. 95, 836 (1991);Multiple quantum effects in double frequency (dt) pulsed NMR experiments on multilevel spin systems are studied. In these experiments, the spin systems are irradiated by two rf fields, applied simultaneously. A general theoretical description of these experiments is presented using the theory of Shirley for time dependent Hamiltonians. Multiphoton resonance conditions are given and time independent fictitious spin-1/2 Hamiltonians are derived using his perturbation theory treatment. With these Hamiltonians, the evolution of the spin systems during df irradiation is approximated. The example of df NMR experiments on an I = 1/2 spin system is discussed. High order perturbation theory is developed to describe the time evolution of this spin system at a three photon resonance. Accurate computer calculations are performed to examine this time evolution. Of NMR experiments are performed on the single 31p(I = 1/2) transition of phosphoric acid to check the theoretical results. The three photon resonance condition for these measurements is studied as a function of the rf irradiation intensities and of the resonance offsets of the two frequency components of df irradiation fields. Special NMR pulse cycles are used to study the dependence of the phase of the coherence created by df pulses on the initial rf phases of the two frequency components. Spinecho type of experiments are developed to detect the spiral motion of the magnetization vector of the I = 1/2 spin system at the three-photon resonance.

Multi-Frequency Resonances in Pure Multiple-Pulse NQR

“…As follows clearly from the comparison of expressions (23), (24) decreases with number of photons [10,19,25], the intensity of the resonance signal diminishes quickly with number of the mode. A peculiarity of the excitation scheme proposed in the present paper is that, along with multiphoton transitions, there are direct transitions between dressed spin states with (n − m) > 1 .…”

“…where ε α = α (ω e − Ω) , b αβ m−n = b m−n are the Fourier coefficients determined in (10). The first term in (32) is diagonal, while the second one is off-diagonal.…”

“…Therefore all resonance transitions between different states of the Hamiltonian (32) can be excited in the straight way without involving intermediate states as it is used in the scheme of multiphoton excitation proposed in [10,19,25] .…”

“…Multiple resonance modes of higher orders have been detected by microwave spectroscopy [6], molecular beam technique [7], optical pumping [8] and observed previously in NMR experiments [9][10][11][12][13]. However the amplitude of these resonances decreased abruptly with the mode order of the resonance.…”

“…The Floquet theory [17] is a power method widely used in NMR spectroscopy for solving time-dependent problems [10,19]. On the one hand, this approach uses the advantages of the secondary quantization method resulting in the time-independent Hamiltonian.…”