Sensitive photoacoustic overtone spectroscopy of acetylene with a multipass photoacoustic cell and a colour centre laser at 1.5 μm

Sensitive Doppler-limited overtone spectra of acetylene in the spectral region 6300–6400 cm^?1 have been recorded using a single mode NaCl---OH^? colour centre laser and a radial resonant photoacoustic multipass cell. We observed some very weak bands which have not been recorded up to now. By comparing our signal strength with direct absorption measurements of some stronger bands, we were able to calculate a minimum detectable absorption coefficient _min ≈ 10^?9 cm^?1.