Electron spin resonance studies of elementary processes in radiation- and photo-chemistry. Part 11.—Radical reactions of α-aminobutyric acid between 26 and 440 K

Abstract

Irradiation of α-aminobutyric acid single crystals with ⁶⁰Co γ-rays at 26 to 77 K results in the trapping of the protonated molecular-anion CH₃CH₂CH(NH₃⁺)CO₂H^–(R1). During thermal annealing to 440 K, six further radicals are formed, including CH₃CH₂ĊHCO₂H(R4), ĊH₂CH₂CH(NH⁺₃)CO^–₂(R2), CH₃ĊHCH(NH⁺₃)CO^–₂(R3) and (CH₃)₂ĊCO₂H(R7). The conversion of R1 to R4 and then to R2 and R3 occurs between 100 and 145 K by processes involving only 8–17 kJ mol^–1“activation” energy and determined largely by steric considerations. The conversion of R3 to R7 has been followed isothermally between 330 and 365 K and the decay of R7 between 390 and 430 K. These processes have “activation” energies of 71 ± 7 and 83 ± 5 kJ mol^–1 respectively and are likely to involve some translational motion of the radicals. A possible mechanism for the radiolysis is discussed.