Swept-frequency two-pulse phase modulation (SWf-TPPM) sequences with linear sweep profile for heteronuclear decoupling in solid-state NMR

Recently, a pulse scheme for heteronuclear spin decoupling in solid‐state NMR, called swept‐frequency two‐pulse phase modulation (SWf‐TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency‐sweep profile can be varied to achieve optimal efficiency for crystalline and liquid‐crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SWf‐TPPM sequences with tangential sweep profiles (SWftan‐TPPM) and linear sweep profiles (SWflin‐TPPM). Using the 13CH2 resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut‐off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise. Copyright © 2008 John Wiley & Sons, Ltd.