Absolute 12C16O2 transition frequencies at the kHz-level from 1.6 to 7.8 µm

- Transition frequencies were measured for CO2 lines in the (30013)←(00001) band.
- These absolute transition frequencies were linked to a cesium atomic clock.
- A global fit was performed to numerous CO2 bands in the near- and mid-infrared.

Absolute transition frequencies were measured for a series of transitions in the (30013)←(00001) near-infrared 12C16O2 band. These measurements were referenced to a cesium atomic clock through the use of an optical frequency comb. Combined standard uncertainties as low as 18 kHz (6×10−7 cm−1) were achieved. Importantly, deviations as large as 5 MHz were observed relative to the HITRAN 2008 database. These measurements were then included in a global fit of 416 CO2 mid-infrared and near-infrared measurements each of which was absolute. The resulting spectroscopic parameters provide a series of secondary frequency standards with kHz-level uncertainties across a wide frequency range and should significantly improve spectroscopic retrieval algorithms for space-based measurements of atmospheric CO2.