SINGLET-TRIPLET ABSORPTION BANDS OF METHYL-SUBSTITUTED ETHYLENES

In the absorption spectra of the methylated ethylenes propene and 2-methylpropene in the gas state plus 70 atm of oxygen, banded structures are found which can be identified as triplet ← singlet (T ← N) transitions analogous to that found for ethylene itself. A similar absorption but without structure is found for trans-butene. At shorter wavelengths, and also even at longer wavelengths in 2-methyl-2-butene and in 2,3-dimethyl-2-butene vapor in the presence of 70 atm of oxygen, relatively strong absorption was found which can probably be attributed to contact charge-transfer transitions from the ethylene to O2. This absorption defeated attempts to determine by oxygen enhancement whether the extremely weak bands which have been observed by others at 2100-2500 Å on the long wavelength side of the Rydberg bands of the methylated ethylenes are the triplet ← singlet analogs of the Rydberg bands. To determine the location of the T ← N bands of 2-methyl-2-butene and 2,3-dimethyl-2-butene, enhancement in the liquid state by CH2Br2 was used.