Laser excitation of high CH stretching overtones has been used to induce the isomerization of l-cyclopropylcyclobutene (CYCB) to 2-cyclopropyl-l, 3-butadiene. Values of the unimolecular isomerization rate constant, k (E), have been measured for excitation of the fifth cyclobutenyl and cyclopropyl methylenic CH stretching overtones. The values of k (E) depend only on total energy and do not show any identifiable dependence on which type ...