The HD spectrum near 2.3 μm by CRDS-VECSEL: Electric quadrupole transition and collision-induced absorption

- Exhaustive review of the HD transitions reported in the literature up to 20,000 cm−1.
- First spectra recorded by high sensitivity CRDS-VECSEL near 2.3 μm.
- First detection of the S(3) quadrupole electric transition of HD fundamental band.
- Agreement with advanced ab initio calculations within experimental uncertainties.
- Measurement of the HD collision induced absorption (CIA) near 4360 cm−1.

The HD absorption spectrum is investigated near 2.3 μm with the help of a newly developed Cavity Ring Down Spectrometer (CRDS) using a VECSEL (Vertical External Cavity Surface Emitting Laser) as light source. The HD CRDS spectra were recorded for a series of ten pressure values in the range 50-650 Torr. The sensitivity of the recordings - noise equivalent absorption of the spectra on the order of αmin ≈ 5 × 10−10 cm−1 - has allowed for the first detection of the S(3) quadrupole electric transition of the HD fundamental band, at 4359.940 cm−1. The line center determined with an uncertainty of 0.002 cm−1 agrees with the most recent theoretical calculations. The retrieved value of the line intensity (2.5 × 10−27 cm/molecule at 296 K) agrees within 12% with the ab initio values included in the HITRAN spectroscopic database. We take the opportunity of this contribution to provide an exhaustive review of seventy-three HD absorption lines previously detected up to 20,000 cm−1.From the pressure dependence of the baseline of the CRDS spectra, the binary absorption coefficient of the HD collision induced absorption band is determined to be 1.17(4) × 10−6 cm−1amagat−2 at 4360 cm−1.

212