Transition probabilities for the W^3Δu–B^3Πg system of molecular nitrogen

The Einstein transition probability of spontaneous emission for the (0 ← 2) band of the W3Δu ← B3Πg system of nitrogen has been determined by measuring its intensity relative to that of the (2 → 4) band of the B3Πg → A13Σu+ system (1PG), whose transition probability is known. Both infrared bands have the same initial level, B3Πgν = 2. The spectrometer was calibrated for relative intensity with a blackbody emitter at 1273 K. Possible errors from geometrical factors were checked by comparison of the measured relative intensities of the 5 → 3 (Paschen β) and 5 → 4 (Brackett α) H i lines with their theoretically known line strengths. The intensity measurements yield a value of A = 772 s−1 for the (0 ← 2) band of the W3Δu ← B3Πg system, which leads to a value for the electronic transition moment R = 1.89 D.