The intensity of the 105–000 transition of HCN

Abstract
We have remeasured the intensity of the anomalously strong 105–000 band in HCN using long-path length absorption and a cw dye laser. Our initial measurement of this intensity using calibrated intracavity photoacoustic spectroscopy was challenged by a low-resolution photoacoustic spectrum which gave a ratio of intensity of the 105–000 to the 006–000 band that was close to the ratio of 1.5 predicted by theory. Our present result of 16.7 cm/mol, is 20% larger than our earlier result, yielding an intensity ratio of the 105–000 to the 006–000 of 7, which increases the disagreement with theory.