Electron spin resonance (e.s.r.) observations of squid melanin have been conducted over the temperature range 500 degrees K to 4.2 degrees K, and the effect of various chemical treatments of the melanin upon the e.s.r. spectrum has been studied. The findings have shown that the paramagnetism of this melanin follows the Curie Law from 500 degrees K to 4.2 degrees K, that the spin signal can be eliminated by the addition of Cu(++) to the melanin, and that the optical and e.s.r. absorptions of melanin are independent since either can be reduced or eliminated without affecting the other. Similar studies on synthetic melanins produced by autoxidation or by enzymatic oxidation of a number of biphenols were carried out. It was found that the e.s.r. signals of these synthetic melanins were strikingly similar (with respect to line width, line shape, and g-value) with those of squid melanin. It is concluded that the unpaired electrons observed are associated with trapped free radicals in the melanin polymer, that the biosynthesis of melanin may involve a free radical mechanism, and that these physical data are in accord with the concept of Nicolaus that melanin is a highly irregular, three-dimensional, polymer.

A 100-fold increase in the fluorescence emission of crystalline tetracene is observed on cooling from room temperature to 4°K. Phase transformations and lattice distortions are reflected in a drastic change of the emission spectra: the high-temperature modification has an emission that resembles closely tetracene dimer fluorescence while the low-temperature modification fluorescence is nearly a mirror image of the absorption spectrum. The changes in the quantum yields are interpreted on the basis of the Dexter–Fowler model which predicts a considerable difference in the rates of radiationless transitions from different vibronic states.

It is shown that tetracene dimerizes. The association equilibrium constant K=2.2×10−4 exp(7.2/RT) for 283°≥T≥168°K. The absorption and emission spectra of the dimer are compared with those of the monomer and of crystalline tetracene. The dimer and the crystal spectra are similar.

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The alpha-induced decomposition of ammonia was studied as a function of pressure (70–740 mm) and intensity. The ion yield was found to increase both with increasing intensity and decreasing pressure. The variation with intensity was more pronounced below 200 mm than at higher pressures. Several models were examined to account for the experimental results. The decrease in the yield with increasing pressure was due to the deactivation of NH3* generated by the reaction NH2+H→NH3*. At all intensities used in this work, gas phase ion recombination was negligible. The positive ions were assumed to react with NH3 to form NH4+ which was neutralized at the wall. At sufficiently high pressure and intensity, the NH2 radicals reacted homogeneously in the gas phase, but at low pressure and intensity, wall reactions became important. This ``intensity'' effect was caused by the ions and does not appear in photolysis. The ion-molecule reactions generate the NH4+, the pressure controls the diffusion process, and the intensity determines the relative importance of the gas phase and the wall reactions. The intensity effect is a function of all four variables. On the basis of the reaction scheme and the present knowledge of the mass spectrum, it was possible to calculate a lower limit for the ion yield.