DYNAMICS OF ORGANIC-REACTIONS IN DIFFERENT ENERGY-LEVELS FROM CRYOGENIC RATE DATA

Experimental rate data for seven organic reactions at cryogenic temper atures have been interpreted to provide information about the dynamics of the reactant molecules in different energy levels. The observed th ermal rate constants were assumed to equal sums over quantized energy levels of the specific rate constant for a level multiplied by the Bol tzmann population for the level. The model has been analyzed to find r elationships between microscopic behavior and experimental observables , such as the isokinetic point, the point of maximum curvature, the ac tivation energy, the pre-exponential factor, and the kinetic heat capa city spectrum. By least squares fitting, the energy gaps between the a ctive levels were found to be 950 +/- 50, 1120 +/- 40, 230 +/- 30, 580 +/- 40, 440 +/- 30, 700 +/- 70, and 630 +/- 50 cm(-1) for the inversi ons of the oxiran-2-yl and [2-D]-1,3-dioxolan-2-yl radicals, for hydro gen atom transfer in irradiated dimethylglyoxime, tripler 2-(2'-hydrox yphenyl)benzoxazole, and 2- (2'-hydroxy-4'-methylphenyl)benzoxazole, a nd for deuterium atom transfer in tripler 2-(2'deuteriooxyphenyl)benzo xazole and 2-(2'-deuteriooxy-4'-methylphenyl)benzoxazole respectively. The specific rate constants times the degeneracies of the dominant, e xcited, reactive levels were 3.8 +/- 0.2, 5.0 +/- 0.1, 2,8 +/- 0.2, 2. 8 +/- 0.1, 2.5 +/- 0.1, 4.8 +/- 0.3, and 4.6 +/- 0.2 orders of magnitu de, respectively, faster than the corresponding quantities for the low er level. Inversion of the oxiranyl and dioxolanyl radicals may be lim ited by the rate of vibrational excitation.