The electronic spectrum of methyleneimine

Cavity ring-down spectroscopy (CRDS) has been employed to observe the electronic spectrum of methyleneimine (H2CNH), which is the simplest imine compound. This species was prepared by the pyrolysis of methyl azide. The CRDS signals over the wavelength range 234 to 260 nm were recorded as a function of the temperature of a heated section of tubing upstream of the CRDS cell. The absorption spectrum of methyleneimine was found to be broad and structureless, with an absorption maximum near 250 nm. The absorption cross section of methyleneimine was estimated by comparison with the absorption spectrum of methyl azide. The 118-nm I-photon photoionization and the UV multiphoton ionization mass spectra of a molecular beam of unpyrolyzed and pyrolyzed methyl azide were also investigated. The strongest mass peak in the multiphoton ionization of methyleneimine was found to be m/e = 28, corresponding to H2CN+ or HNCH+. These results are used to interpret the excited electronic states and photochemistry of methyleneimine.