Knowledge Bank

The Einstein transition probability of spontaneous emission for the ($0\leftarrow 2$) band of the $W\leftarrow B$ system of nitrogen has been determined by measuring its intensity relative to that of the (2 $\to$ 4) band of the $B\to A$ system (1PG), whose transition probability is known. Both infrared bands have the same initial level, v = 2. A relative intensity calibration of the spectrometer was carried out with a black-body emitter. The intensity measurements yield a value of A = 772 $sec-1$ for the (0 $\leftarrow$ 2) band of the $W\leftarrow B$ system, which leads to a value for the electronic transition moment of R = 1.89 Debye. Radiative lifetimes have been calculated for a number of levels of the W state. These lifetimes are characterized by an unusually large range of values as a result of the dominance of the frequency factor in the transition probabilities. Where collisional deactivation may be neglected, there arises the question of competition between low frequency permitted transitions and high frequency forbidden transitions originating in the $W3\Delta u$ state. In order to deal quantitatively with the question of possible ultraviolet emission from the $W3\Delta u$ state, a study of absorption spectra was undertaken for neighboring bands in the 1500 \AA region. These bands have as their upper electronic states the $A3\Sigma u+$, the a^{\prime} $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma u$-, and the $W3\Delta u$ of $N2$. Comparison of their absorption intensities permits an assessment of the $W3\Delta u$ - $X1\Sigma g+$ transition probabilities. The relative importance of the $W\to B$ and $W\to X$ systems in emission may thereby be estimated.