The radical anions of methyl-, methoxy-, fluoro-, cyclopropyl-, and cyanocyclooctatetraene were generated by electrolytic reduction of the neutral compounds in liquid ammonia. The electron spin resonance spectrum of each radical anion is assigned, and a clean even-odd alternation of the spin densities is observed in each. This alternation can be correlated with the electronic properties of the substituent. For the radical anions of methyl-, methoxy-, and cycl opropyl cycl ooctatetraene, the temperature dependence of the coupling constants is reported. The results are accounted for in terms of vibronic mixing and Jahn-Teller distortions, and are discussed in relation to INDO calculations.
Time resolved photoacoustic spectroscopy represents a promising new approach to the study of time resolved absorption with picosecond time resolution. The sensitivity of photoacoustic detection permits investigation of dilute and fluorescent samples which are difficult to study by conventional flash photolysis. Theory shows that quantitative measurements of important transient properties and new insights into photochemical and photophysical dynamics can be obtained by measuring heat deposition as a function of probe fluence. Experimental determinations of absorption and stimulated emission cross sections, and lower limits for rates of nonradiative relaxation of highly excited states, are presented.
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