A new technique is proposed to carry out Signal Amplification By Reversible
Exchange (SABRE) experiments at high magnetic fields. SABRE is a method, which
utilizes spin order transfer from para-hydrogen to the spins of a substrate in
transient complexes using suitable catalysts. Such a transfer of spin order is
efficient at low magnetic fields, notably, in the Level Anti-Crossing (LAC)
regions. Here it is demonstrated that LAC conditions can also be fulfilled at
high fields in the rotating reference frame under the action of an RF-field.
Spin mixing at LACs allows one to polarize substrates at high fields as well;
the achievable NMR enhancements are around 360 for the ortho-protons of
partially deuterated pyridine used as a substrate and around 700 for H2 and
substrate in the active complex with the catalyst. High-field SABRE effects
have also been found for several other molecules containing a nitrogen atom in
the aromatic ring