Nanosecond flash photolysis of b-nitronaphthalene (b-NOnClaH7) in nonpolar and polar solvents shows a transient species with maximum absorption and lifetime dependent on solvent polarity. In deaerated n-hexane the absorption maximum and lifetime (l/k) are 425 nm and 530 nsec, while in deaerated ethanol the corresponding values are 470 nm and 1.7 psec. This transient absorption is attributed to the triplet excited state of b-NOzCloH,, and the observed red shift as well as its longer lifetime in polar solvents are indicative of the intramolecular charge transfer character of this state. The change of dipole moment accompanying the transition T1-iT,, as well as rate constants for electron and proton transfer reactions involving the T I state of h-NOaCloH7, were determined. The spect.roscopic and kinetic data obtained in this work indicate that, the triplet state of b-NOnClaH7 behaves like a n-r* state in nonpolar media, while in polar solvents the n-r* character of the state is reduced with a simultaneous increase in the charge transfer character.
difficulties in making H atom concentration measurements. The hydrogen atoms are probably trapped in multiple sites with different relaxation times at the different sites.11 Since some of these sites are saturated, intensity measurements using our present apparatus are unreliable. When the microwave power is reduced to a low level, the HCO signal is reduced below the threshold detection level without completely alleviating the H atom saturation.Although other mechanisms cannot be ruled out, it is postulated that reaction mechanisms 3 and 4, the H K. Suryanarayanan and Suryanarayana Bulusu atom abstraction from formaldehyde and the recombination of H atoms and CO molecules, are the most probable mechanisms for the increase of formyl radicals at 87°K.
Flash photolysis of 2,4,6‐trinitrotoluene solutions (TNT) indicates a photochemically induced isomerization leading to the aci‐quinoid isomer
with an absorption maximum at 460 nm in nonpolar solvents, or the conjugate base
of the aci‐quinoid isomer with absorption maxima at 500, 540, and 630 nm in polar solvents. Both species, the quinoid isomer and the conjugate base, have transient existence and their identification was based on detailed spectroscopic and kinetic studies presented here. The magnitude of the negative charge on the transient conjugate base was determined with salt effect experiments and found to be equal to unity.
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