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

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 ${}^2\Sigma$ electronic state of CsO; for Na + NO₂, probably a ${}^2\Pi$ 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 ${}^2\Pi$ for LiO (the only species which had been previously observed) to ${}^2\Sigma$ 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 Ų. For the CH₃NO₂ reactions differential surface ionization is applicable. Again the reaction cross sections are ∼ 100 Ų 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 $\mathrm{R}\mathrm{\hspace{0.17em}=\hspace{0.17em}i‐}{\mathrm{C}}_5{\mathrm{H}}_{11}$ and $\mathrm{R}\mathrm{\prime \hspace{0.17em}=\hspace{0.17em}}{\mathrm{C}}_2{\mathrm{H}}_5$ ), which give diamagnetic products with yields very similar to CH₃NO₂, and N₂O and R″OOR″ (with $\mathrm{R}\mathrm{″\hspace{0.17em}=\hspace{0.17em}t‐}{\mathrm{C}}_4{\mathrm{H}}_9$ ), for which only paramagnetic species were observed.