High accuracy line positions of the ν 1 fundamental band of 14 N 2 16 O

Abstract

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Optical frequency comb Fourier transform spectroscopy of 14N216O at 7.8 µm

“…A clear systematic discrepancy is visible, though remaining within the HITRAN frequency uncertainty of 3 MHz. Furthermore, this clear systematic tendency closely follows that reported in a recent work by AlSaif et al [21], using a combreferenced external-cavity QCL, shown by the red markers. Similar to that study, we fit a model based on the effective ro-vibrational Hamiltonian (see Eq.…”

“…We fit the vibrational term value G v , the rotational constant B v , and the quartic and sextic centrifugal distortion constants D v , H v of the vibrationally excited state (fixing L v to 0) and fixed the ground-state rotational and centrifugal distortion constants to those determined by Ting et al [39]. The fitted upper-state constants of the ν 1 band are presented in Table 2, and compared to those obtained by AlSaif et al [21]. Except for G v , the retrieved upper-state constants from our work and Ref.…”

“…Similar to that study, we fit a model based on the effective ro-vibrational Hamiltonian (see Eq. ( 1) in [21]) to these line positions using the PGOPHER software [38]. We included only the transitions between P(32)-R(34) (i.e.…”

“…Lamperti et al [20] referenced a CW QCL tunable around ~8 µm to a Tm:fiber comb at 1.9 µm through a sum frequency generation scheme, and reported the positions of three lines in the ν 1 band with ~63 kHz uncertainty. AlSaif et al [21] used this comb-referenced QCL to retrieve positions of the P(40) to R(31) lines of the ν 1 band in the Doppler limit with uncertainties below 200 kHz. More recently, they measured the center frequency of the R( 16) line with precision below 50 kHz using sub-Doppler spectroscopy [22].…”

Comb-calibrated sub-Doppler spectroscopy with an external-cavity quantum cascade laser at 77 μm

“…The comparison between line centers obtained from repeated measurements of the same dip returns a statistical uncertainty of 4.5 kHz for the single measurement, which is consistent with a dip signal to noise ratio of about 200 and a sub-MHz dip. The retrieved line center frequency calculated as a weighted mean of the line positions obtained at different power values (38931326476.0(3.5) kHz) differs by 48 kHz from the calculations reported in [20,23], which are declared accurate to within 2.4 kHz, and by 57 kHz from a recent model based on Doppler broadened comb-calibrated spectra [24]. In a worst-case scenario, we estimate at the 50 kHz level the accuracy of our determinations, mainly limited by a residual few-percent asymmetry of the spectral baseline that emerges from the residuals (Fig.…”