High-resolution cavity ring-down study of acetylene between 12 260 and 12 380 cm−1

The cavity ring-down laser method using a continuously tunable titanium:sapphire ring laser with an external high-finesse cavity has been used to record a high-resolution overtone spectrum of a gaseous 12C2H2 sample in the wavenumber region 12 260–12 380 cm−1. A direct non-linear least-squares fitting of the ring-down signal is found to lead to increased sensitivity when compared with the linear-least squares methods. Two new bands have been observed and rotationally analysed. A comparison of the new results with previous theoretical work shows a good agreement.