Differential cross sections have been measured for the reactions ${\mathrm{C}}^{12}({\mathrm{Li}}^6, \alpha ){\mathrm{N}}^{14}$ and ${\mathrm{C}}^{12}({\mathrm{Li}}^7, \alpha ){\mathrm{N}}^{15}$ with the residual nuclei in their ground or first few excited states. The total cross section for the 2.31-Mev $T=1\mathrm{}$ state of ${\mathrm{N}}^{14}$ is 0.1 mb at 4.0 Mev, compared to a cross section of 2.9 mb for the ground state; this violation of the isotopic spin selection rule is probably due to mixing of different isotopic spin states in the compound nucleus ${\mathrm{F}}^{18}$. The differential cross sections for the other levels have general features suggestive of a direct interaction.

• Received 9 February 1962

DOI:https://doi.org/10.1103/PhysRev.126.2137