Molecular Beam Kinetics: Reactions of Alkali Atoms with NO2 and CH3NO2

Abstract

Magnetic and electric deflection analysis of the scattering of Cs + NO2 shows that the principal product is a paramagnetic, polar molecule. Magnetic analysis of the K + NO2 system indicates that the scattered signal is paramagnetic; a similar study of Na + NO2 shows a small yield of diamagnetic product. For the analogous reactions with CH3NO2, the product is diamagnetic and has a pseudo-first-order Stark effect. From these data and thermochemical arguments the principal alkali-containing products are identified as: for Cs + NO2, a 2Σ electronic state of CsO; for Na + NO2, probably a 2Π state of NaO; for M + CH3NO2, almost certainly MNO2 in a singlet state. The NO2 results indicate that the ground state of the MO molecule changes from 2Π for LiO (the only species which had been previously observed) to 2Σ for CsO. The usual differential surface ionization detection fails for Cs + NO2 and consequently only a very rough estimate of the scattering is obtained; this indicates that the total reaction cross section is ∼ 100 Å2. For the CH3NO2 reactions differential surface ionization is applicable. Again the reaction cross sections are ∼ 100 Å2 and increase as Na→K→Cs. The c.m. product angular distribution is broad, with about the same intensity in the forward and backward hemispheres. These results are discussed in terms of the electronic structure of the reactant and product molecules and contrasted with reactions of alkali atoms with halogen-containing molecules. Scattering of related molecules has also been studied briefly, including RONO and R′ONO2 (with R = i-C5H11 and R′ = C2H5), which give diamagnetic products with yields very similar to CH3NO2, and N2O and R″OOR″ (with R″ = t-C4H9), for which only paramagnetic species were observed.