Knowledge Bank

To take full advantage of recent improvements in the accuracy obtained in collision-induced absorption line shape measurements of the acetylene $\nu 1+\nu 3$ combination band, independent and accurate knowledge of the positions of weaker, overlapping hot band transitions is required. We have used cavity-enhanced saturation-absorption spectroscopy together with a frequency-comb referenced, extended cavity diode laser to determine Doppler-free transition frequencies for the $\nu 4$ and $\nu 5$ hot band transitions in this region . A laser intensity dependent asymmetry in the sub-Doppler saturation line shape is observed, and will be discussed in terms of the intra-cavity beam geometry. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences.