Pulse-transient adapted C-symmetry pulse sequences.

In solid-state NMR, pulse sequences make often use of pulses which are short compared to the recovery time of the probe head. Especially, rotorsynchronized dipolar recoupling experiments under magic-angle-spinning conditions can profit from the use of very high pulse amplitudes which in turn will reduce the length of the individual pulses. In this contribution we show that C-symmetry based pulse sequences used for double-quantum filtering experiments can strongly be influenced by pulse transients. We analyze the origin of pulse transients and show that the quadrature component can be minimized by cable-length variation which causes a mutual cancellation of probe-external and internal contributions. We implement and test a model to investigate the influence of pulse-transients by numerically exact calculations of the spin-density matrix allowing for composite pulses consisting of slices which are short compared to the circuit recovery time-constant. Moreover we introduce a phase-tuned C-element, which can be applied to γ-encoded experiments from the C-symmetry class, to reconstitute an almost ideal performance of the sequence. We have validated the modified transient-adapted pulse sequences theoretically on the basis of numerically exact calculations of the spin-dynamics. While comparably easy to apply the scheme proved also robust in practical application to (15)N, (13)C and (31)P double-quantum filtered experiments and leads to a significantly increased conversion efficiency.