High accuracy line positions of the ν₁ fundamental band of ¹⁴N₂ ¹⁶O

The ν₁ fundamental band of N₂O is examined by a novel spectrometer that relies on the frequency locking of an external-cavity quantum cascade laser around 7.8 µm to a near-infrared Tm:based frequency comb at 1.9 µm. Due to the large tunability, nearly 70 lines in the 1240–1310 cm⁻¹ range of the ν₁ band of N₂O, from P(40) to R(31), are for the first time measured with an absolute frequency calibration and an uncertainty from 62 to 180 kHz, depending on the line. Accurate values of the spectroscopic constants of the upper state are derived from a fit of the line centers (rms ≈ 4.8 × 10⁻⁶ cm⁻¹ or 144 kHz). The ν₁ transitions presently measured in a Doppler regime validate high accuracy predictions based on sub-Doppler measurements of the ν₃ and ν₃-ν₁ transitions.