Overtone Vibrational Photochemistry of Quadricyclane

Article abstract of DOI:10.1021/j100314a018

The photochemistry of quadricyclane (Q) was explored by single-photon excitation to high vibrational levels.Spectra of the ν = 4-7 carbon-hydrogen overtones were recorded by using intracavity absorption and photoacoustic detection.These spectra were compared to the infrared fundamental spectrum and assigned.Excitation of the ν = 5 and ν = 6 bands of cyclopropanoid and methylenic hydrogens leads to reaction.At least one intermediate, probably a vibrationally excited form of norbornadiene (N), must be involved because partitioning among various reaction channels is pressure dependent.Apparent rate constants were measured and correlated with variations in pressure according to the Stern-Volmer relationship.Experimental values were compared with rate constants calculated by RRKM theory.Although there is a modest amount of "excess" reaction observed for the lowest excitation energies above threshold, overall evaluation provides no significant evidence for concentration of energy in localized modes for times that are long compared with reaction times.