COHERENT RAMAN BEAT EPR WITHOUT PREEXCITATION PULSES

Coherent Raman beat electron paramagnetic resonance (EPR) spectra with out application of one or more excitation pulses have been observed in the EPR spectrum of the tetramethyl-1,4-benzosemiquinone anion radica l in a frozen mixture (50:50) of protonated and fully deuterated isopr opyl alcohol at 4.2 K. The free nuclear transition frequencies of hydr ogen and deuterium and the small quadrupole coupling of 146 kHz of the deuterium could be measured with high sensitivity and precision (line width = approximate to 40 kHz). The modulation amplitudes of the deut erium matrix lines at 2.2 MHz, as a function of the observer power, re veal a distinct resonance behavior coinciding with the frequency of th e transient nutations, that is, when the Rabi frequency is approximate ly equal to the nuclear precession frequency. These observations sugge st that the mechanism of coherence transfer between the electron and n uclear spin systems is related to the Hartmann-Hahn effect.