Electronic Excitation in Fast Collisions of Na with SO2 and NO2

A sputtered Na beam has been used to investigate collisionally induced electronic excitation in scattering with SO₂ and NO₂. Light from the radiative decay of excited electronic states was observed at several wavelengths, and measurements were made of the excitation cross sections as a function of the center‐of‐mass collision energy in the range 1–30 eV. In both scattering systems, the most intense light measured originated from the Na ${\text{(3}}^2{\text{P→3}}^2\mathrm{S)}$ D line. Light from the ${\text{(4}}^2{\text{D→3}}^2\mathrm{P)}$ Na transition was observed, but its intensity was more than an order of magnitude smaller than that of the D line. Emission also occurred from transitions with long radiative lifetimes $\text{(∼40\hspace{0.17em}μ}\sec )$ . This emission is probably due to the $B_1{\mathrm{\to A}}_1$ molecular transitions of SO₂ and NO₂. The results have been discussed in terms of a potential curve‐crossing mechanism which seems to satisfactorily explain collisionally induced alkali atom excitation. For the molecular emission, an alternate mechanism has also been considered which involves vibrational coupling of the A₁ and B₁ states.