Electronic spectra in the 2100-2500 8, region, were reported for the allyl radical, the P-methallyl radical, the cc-methallyl radical, the p-ethallyl radical and the cyclopentenyl radical. The vibrational structures of the allyl and P substituted radicals indicate that in the main regions of absorption, the a(C-13) stretching frequency is excited. A single band progression observed in flashed allyl cyanide, was tentatively assigned to a free radical derived from pyrrole.
From direct observation of the CH3, CH3S, CHzS and S2 produced in the flash photolysis of CH3SSCH3 (-1950 A) it was concluded that the primary processes are : CH3SSCH3 +hv +CH3SSCH; CH3SS* + CH:, /I CH,SSCH*,+2CH,S CH2S+CH3SH CH3SS" +CH3 + Sz IM +CH,SS.
The far ultra-violet continuum of nitric oxide was assigned to the dimer by obtaining the following experimental evidence : (a) the intensity of the spectrum is proportional to; (b) the possibility that the carrier may be some other known oxide of nitrogen was eliminated ; (c) from the temperature dependence the enthalpy change accompanying dissociation was 2.24 (f 0.1) kcal/mol (100-140 K), in good agreement with 2.4 (f0.2) kcal/mol deduced from the dimer infra-red intensities ; ( d ) approximate upper and lower limits to the dissociation constant, and the temperature dependence, were consistent with Guggenheim's method of analyzing the second virial coefficients by means of the principle of corresponding states.An absolute scale of dissociation constants was fixed from the excess of the reduced second virial coefficient at its normal boiling point, and the temperature dependence found spectroscopically. The dissociation energy of the dimer is 1.6 (fO.l) kcal/mol. Evidence for substantial population of excited states of the dimer at 300 K was discussed. The dimer continuum exhibits a maximum at 2050& and the oscillator strength of the system was recorded as 0.26.
The integrated absorption of the P1-X transition of the methyl radical (2160 A) and the B-X transition of the allyl radical (2100-2400 A) were compared, in the flash photolysis of butene-1.From thef-value of the CH3 band, the oscillator strength of the allyl transition was recorded as 0.140 (rf0.028). The rate coefficient for recombination of allyl radicals was in the range 8.5(f3)x loi2 cm3 mol-l s-l.
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