Radiationless transitions between states of different multiplicity are considered with special reference to conversion between triplet and singlet energy levels. Rates of this conversion have been measured for naphthalene and anthracene and rate constants are given for the fist-order intramolecular process, the second-order process involving two triplet molecules and also of quenching by other species, particularly paramagnetic ions. It is established that the first-order rate is strongly viscosity dependent and this is attributed to a structural difference between the two states.Conversion from the triplet state is induced by paramagnetic molecules and ions but the quenching rate constant shows no correlation with magnetic susceptibility. A general theory of " paramagnetic quenching " is proposed in which the function of the quenching molecule is one of overall spin conservation. a b c d e FIG. 1 .-Oscillographic records of the decay of triplet naphthalene in (a) n-hexane, (6) water, (c) ethylene glycol, ( d ) paraffin r] = 33 cp, ( e ) paraffin 3 = 167 cp. Time units : msec.
The red glow emitted from partially dissociated chlorine has been shown to occur via the termolecular reaction, k 1 4 c1+ c1* + Clz+ c1; + Cl., followed by the emission process, From measurement of the absolute quantum yield of emission, and quenching of the emission by Cl2, k14 = 0.94 x 1015 cm6 mole-2 sec-1, and the radiative lifetime of Clt = l/kls> 3 x 10-7 sec.
Addition of argon to the chlorine gave the reaction rate forkl8 c1+ C1* -t-Ar+ Cl; + Ar as klg = 2.35 x 1014 cm4 mole-2 sec-1. concentrations ; the process occurs via the two consecutive reactions : Rates of recombination of chlorine atoms were investigated using the red emission to measure atom k9 k-9 c1+ c 1 2 + c 1 3 kltl C13+C1---tCl~+C1~. k 9 = 9.09 x lo7 cm3 mole-1 sec-1, k-9< 7.6 x lo5 sec-1, and under experimental conditions [C13] > 1 . 2 ~ 10-5 [Cl]. Recombination of chlorine atoms with argon as third body has given the overall termolecular rate constant for the reaction, k23 C1+ C1+ Ar-+ C12+Ar as 4-25 f0.8 x 101s cm6 mole-2 sec-1.
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