The c.hfl-value of the NO δ(0, 0) band by the line absorption method

The resonance-line absorption method has been applied to the isolated but unresolved (0, 0) band of the NO δ system, C²Π - X²Π. The light source was the N + O radiative recombination afterglow in a discharge flow system. This is an optically-thin source of δ(0, 0) emission, with known rotational temperature and Doppler width, uncontaminated with overlapping ε bands. Corrections for effects of accidental line overlap within the band and perturbation between the C and B states have been applied in comparing observed and computed band fractional absorption curves. For the δ(0, 0) band, this comparison gives c.hfl = (2·2 ± 0·3) × 10^-3. Our result is compared with previous measurements obtained by four other independent methods.