  A method is implemented to perform "fast" adiabatic variation of the spin
Hamiltonian by imposing the constant adiabaticity condition. The method is
applied to improve the performance of singlet-state Nuclear Magnetic Resonance
(NMR) experiments, specifically, for efficient generation and readout of the
singlet spin order in coupled spin pairs by applying adiabatically ramped
RF-fields. Test experiments have been performed on a specially designed
molecule having two strongly coupled C-13 spins and on selectively isotopically
labelled glycerol having two pairs of coupled protons. Optimized RF-ramps show
improved performance in comparison, for example, to linear ramps. We expect
that the methods described here are useful, not only for singlet-state NMR
experiments, but also for other experiments in magnetic resonance, which
utilize adiabatic variation of the spin Hamiltonian.
