Construction of a time-resolved multiple resonance spectrometer

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We built a time-resolved multiple resonance spectrometer equipping a high power raido frequency amplifier (Kalmus 166LPX1, power output : 1 kW (pulse) and 200 W (CW), frequency range : 5-86 MHz) and a synthesizer (Anritsu MG250113, frequency 1-600 MHz). Transient signals are directly taken into a digital storage oscilloscope (Tektronix 2440, DC-100MHz) and a personal computer (Ricoh PS/V2410NAB for data analysis. Both microwave and radio frequency can be applied in the pulse mode by using an X-band pulsed EPR spectrometer (Bruker ESP380E).We applied the system for the measurements of the ENDOR spectra of transient free radicals and the excited triplet states generated by laser pulse irradiation. The present study clearly shows that this system plays an important role in photochemistry, because the spectral resolution is highly improved. The electronic structure and deviation of the geometry in the excited triplet states from the ground state can be clarified from the distribution of the unpaired electron spins. It was shown that spectral sensitivity severely depends on the cavity-helix arrangement. The double resonance technique is complementary to electron spin echo technique, that is, the former is powerful for the strong coupling system between an electron spin and nucleuses while the latter for weak coupling system.