Direct measurement, by intracavity laser spectroscopy, of the population difference for the b–X transition in the NF radical

An intracavity laser spectroscopy method was employed in recording for the first time the absorption spectrum of the NF radical in the vicinity of the b–X transition. Experiments showed that the method could be used successfully in direct measurements of the population difference. When the duration of a dye laser pulse was 1.3 μs, the minimum recorded population difference was 3.5×10¹⁵ cm^-3. The rate constant for the NF(X) +NF(X) process was determined: it was (5.5 ± 1.5)×10^-12 cm³ s^-1.