The present paper reports a theory of stimulated polarization of nuclei (SNP) in a switched external magnetic field formulated for the first time. The Laplace transform of the SNP signal with respect to the delay time t o of the field switching is calculated for arbitrary molecular motion of radicals in solution. The result is expressed in terms of the quadratures of the Green functions specifying the character of the motion. Within the framework of diffusion and phenomenological two-positional models of the relative motion, the analysis of the influence of the delay time of external field switching on the spectral line intensity and shape has been conducted. High sensitivity of the line intensity to the character of the relative molecular motion has been predicted.