Acetylene weak bands at 2.5 μm from intracavity Cr2+:ZnSe laser absorption observed with time-resolved Fourier transform spectroscopy

The spectral dynamics of a mid-infrared multimode Cr2+:ZnSe laser located in a vacuum sealed chamber containing acetylene at low pressure is analyzed by a stepping-mode high-resolution time-resolved Fourier transform interferometer. Doppler-limited absorption spectra of C2H2 in natural isotopic abundance are recorded around 4000 cm−1 with kilometric absorption path lengths and sensitivities better than 3 × 10−8 cm−1. Two cold bands are newly identified and assigned to the ν1+ν41 and ν3+ν51 transitions of 12C13CH2. The ν1+ν51 band of 12C2HD and 14 12C2H2 bands are observed, among which for the first time ν2+2ν42+ν5-1.