The sensitivity of this assay drops off with probe frequency due to state saturation, a condition in which the population imbalance becomes negligible; that drop-off occurs because the absorption probability is proportional to the state imbalance. The transverse and longitudinal relaxation times affect this technique because it hinges on detecting the results of the flip of high-energy spin states; the frequency of the radiation thus produced is proportional to the chemical shift, which is output of this form of spectroscopy. For 10 points, name this chemical spectroscopic technique in which radiation from magnetized 
The sensitivity of this assay drops off with probe frequency due to state saturation, a condition in which the population imbalance becomes negligible; that drop-off occurs because the absorption probability is proportional to the state imbalance. The transverse and longitudinal relaxation times affect this technique because it hinges on detecting the results of the flip of high-energy spin states; the frequency of the radiation thus produced is proportional to the chemical shift, which is output of this form of spectroscopy. For 10 points, name this chemical spectroscopic technique in which radiation from magnetized molecules is detected via frequency overlap with an applied radio field.
The sensitivity of this assay drops off with probe frequency due to state saturation, a condition in which the population imbalance becomes negligible; that drop-off occurs because the absorption probability is proportional to the state imbalance.
 NMR spectroscopy [accept nuclear magnetic resonance spectroscopy]