Knowledge Bank

The $NO(b4\Sigma -)$ state, in $v=2-5$, has been excited from the $X2II$ ground state by optical pumping from 187 to 205 nm, and detected by $b4-a4II$ Ogawa band emission. This represents the first optical connection between the doublet and quartet systems and provides a foundation for investigations of the kinetics of the quartet states based on selective optical preparation. Simulation, using published spectroscopic $constants1,2$, shows good agreement for the positions of low J transitions. Comparison of the simulated and observed intensities of the 24 rotational branches suggests that the b-X transition moment involves contributions from perturbers of all potential symmetries: $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma ,\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}II,\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta ,\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}II$. The b-X Einstein coefficient is estimated to be about $103s-1$ based on comparison with $B2-X2II$ bands in the same spectral region. We have also investigated predissociation of $b4\Sigma -(v=6)$ and high-J levels of $b(v=5)$, and collisional production of $b4\Sigma -$ following optical excitation of the $A2\Sigma +B2\Pi$, and $D2\Sigma +$ states. As most of the NO(b) radiates to the $NO(a4II)$ state, this study also provides a means of preparing the low-v levels, principally $v=1,2$, of the NO(a) state, whose kinetic importance has frequently been inferred, but for which no direct production scheme has been available.