Abstract
The time-resolved ADMR (absorption-detected magnetic resonance) spectrum of the polymethylene linked biradical generated in the photolysis of α-(xanthene-2-carbonyloxy)-ω-(xanthene-2-carbonyloxy) dodecane is observed at various microwave power. When the lower microwave power is low, the ADMR spectrum is totally negative (the absorbance of xanthyl radical decreases by the microwave irradiation) and is interpreted in terms of the hyperfine structure of the terminal radicals. In contrast with this, the ADMR spectrum obtained at high microwave field consists of two components: central component and wing component. The central component is positive and is interpreted in terms of the deceleration of the intersystem crossing by microwave, which is known as the spin locking. The wing component is negative and the linewidth is much larger than that of the central one. It is ascribed to the transitions from |T+1> and |T−1> states to singlet state having a slight |T0> character. It is proposed that the width of the time resolved spectrum is due to the fluctuation of the exchange integral (modulated exchange integral) by the motion of the polymethylene chain. The time dependence of the central and wing components and the conditions for observation of them are discussed.
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