The statistical analysis of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ collisions has been performed using the spectral density method. Preequilibrium and compound nucleus coherence widths are determined for successive independent energy intervals. The molecular nature of doorwaylike states giving rise to preequilibrium statistical fluctuations is suggested on the basis of coherence energy dependence on the molecular rotation period. The different behavior of elastic and reaction channels is investigated for what concerns molecular state excitation in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ composite systems. The change with energy of the molecular rigid body moment of inertia is considered.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$,${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$), (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $\alpha$); analyzed excitation functions; spectral density method; deduced coherence width energy dependence; considered molecular level excitation.

• Received 4 January 1983

DOI:https://doi.org/10.1103/PhysRevC.27.2688