Analysis of tunable diode laser spectra of the ν4 band of 12C316O2

Abstract

Current-tunable thin-film PbTe diode lasers have been used to obtain Doppler-limited resolution of the ν4 asymmetric stretch band of C3O2 in the region 1565–1600 cm−1. Roughly 70% of the interval was covered using different modes of three lasers, each mode giving a tuning range of 1–3 cm−1. Absolute spectral calibration was obtained from NH3 and H2O, together with the channel spectrum of a 4-cm Ge etalon recorded simultaneously using a double beam technique. Rotational constants were determined for the ν4 fundamental band and five different hot bands associated with the thermally excited low frequency bending mode ν7. The band origin for the ground state transition is 1587.390±0.002 cm−1 and the ν7 hot bands are shifted progressively to lower frequency. The systematic shift of the hot bands was verified independently with temperature difference spectra from a Fourier transform spectrometer.