A method for precise manipulation of non-thermal nuclear spin polarization by
switching a RF-field is presented. The method harnesses adiabatic correlation
of spin states in the rotating frame. A detailed theory behind the technique
is outlined; examples of two-spin and three-spin systems prepared in a non-
equilibrium state by Para-Hydrogen Induced Polarization (PHIP) are considered.
We demonstrate that the method is suitable for converting the initial
multiplet polarization of spins into net polarization: compensation of
positive and negative lines in nuclear magnetic resonance spectra, which is
detrimental when the spectral resolution is low, is avoided. Such a conversion
is performed for real two-spin and three-spin systems polarized by means of
PHIP. Potential applications of the presented technique are discussed for
manipulating PHIP and its recent modification termed signal amplification by
reversible exchange as well as for preparing and observing long-lived spin
states
