The shape of the ground and lowest two excited states of H2NO

Strategy for improved NH2 detection in combustion environments using an Alexandrite laser

A new scheme for NH₂ detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH₂ was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH₃-air flames and on NH₂ radicals generated through NH₃ photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH₂ line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH₂ A²A₁←X²B₁ transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH₂. A general conclusion was that fluorescence interferences need to be carefully considered for NH₂ diagnostics in this spectral region. Excitation for laser irradiances up to 0.2GW/cm² did not result in NH₂ fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH₂ at around 630nm, excitation at 385.7nm showed a factor of ~15 higher NH₂ signal. The improved signal allowed for single-shot NH₂ LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000ppm, suggesting a detection limit around 700ppm. Thus, the presented approach for NH₂ detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.

The ene reactions of nitroso compounds involve polarized diradical intermediates

The ene reactions of nitroso compounds were studied with B3LYP/6-31G* geometry optimizations and energy calculations, along with single point energy evaluations using CASPT2/6-31G** and UCCSD(T)/6-311+G* methods. Reactions of HNO with propene and of MeNO and p-NO2C6H4NO with propene or substituted alkenes were also studied. The reaction mechanism is stepwise and involves a polarized diradical intermediate. The electronic structure of this intermediate is between that of a closed shell polar species and that of a pure diradical, and it is stabilized by polar solvents. A weak C-N bonding interaction combined with a CH-O hydrogen bond leads to heightened barriers to rotation about formally single bonds compared to conventional diradicals. Consequently, rotation is slower than hydrogen abstraction and cyclization to form an aziridine N-oxide. This aziridine N-oxide does not lead to ene products without subsequent ring opening but provides a mechanism for the RNO moiety to translate from one end of the alkene to the other. B3LYP calculations are also able to reproduce kinetic isotope effects and regioselectivity.