Crossed-Beam Chemiluminescence Studies of Some Group IIa Metal Oxides

Chemiluminescence from a beam of Group IIa metals traversing a scattering chamber filled with NO₂ or N₂O gas has been studied as a function of wavelength and pressure. The $\mathrm{Ba}+{\mathrm{NO}}_2$ and the Ba, Sr, and $\mathrm{Ca}+{\mathrm{N}}_2\mathrm{O}$ chemiluminescent reactions are first order in both reactants while $\mathrm{Ca}+{\mathrm{NO}}_2$ and $\mathrm{Sr}+{\mathrm{NO}}_2$ are quadratic in the NO₂ pressure. Cross sections for beam attenuation are about 90–170 Ų for reactions with NO₂ (consistent with an electron‐jump model), while those for N₂O are 15–30 Ų. For the $\mathrm{Ba}+{\mathrm{NO}}_2$ reaction, the chemiluminescence has been assigned to the BaO A ¹Σ−X ¹Σ band system. From the resolved rotational structure it is concluded that with higher v′ excitation, the J′ distribution is characterized by a lower rotational temperature. A lower bound of 131.5 kcal/mole is placed on $D_0^{°}(\mathrm{BaO})$ . For certain reactions the chemiluminescence is weakly polarized. A model involving the partitioning of angular momentum between the rotation and recoil angular momenta of the products is proposed to account for the degree of polarization of the chemiluminescence.