Dissociation Dynamics of Nitrogen Rich Cyclic Compounds

摘要

The photophysics and photochemistry of the nitrogen-rich compounds diazomethane and diazirine were studied both experimentally and theoretically following excitation in the ultraviolet. These molecules were locally stable on their ground potential energy surfaces, but they contained large amounts of nuclear potential energy that could be unleashed upon photoexcitation. Methods for generating these compounds in supersonically cooled molecular beams were developed to facilitate the experimental studies. Several Rydberg states of diazomethane were characterized experimentally and assigned on the basis of theoretical calculations. Couplings among the Rydberg states and other Rydberg and valence states were analyzed experimentally and lifetimes were estimated. Two-photon excitation of diazirine accessed an excited valence state that dissociated promptly to give CH radicals. A unique mechanism involving isomerization to isodiazirine was proposed to explain this result. Other excited states were assigned and characterized by high-level electronic structure calculations. The diazirine ion was found to be unstable and weakly bound, as opposed to the stable cation of diazirine. A revision to the heats of formation of diazirine and diazomethane was suggested.