Optical frequency comb Fourier transform spectroscopy of formaldehyde in the 1250 to 1390 cm-1 range: Experimental line list and improved MARVEL analysis

We use optical frequency comb Fourier transform spectroscopy to record high-resolution, low-pressure, room-temperature spectra of formaldehyde (H₂¹²C¹⁶O) in the range of 1250 to 1390 cm^-1. Through line-by-line fitting, we retrieve line positions and intensities of 747 rovibrational transitions: 558 from the ν₆ band, 129 from the ν₄ band, and 14 from the ν₃ band, as well as 46 from four different hot bands. We incorporate the accurate and precise line positions (0.4 MHz median uncertainty) into the MARVEL (measured active vibration-rotation energy levels) analysis of the H₂CO spectrum. This increases the number of MARVEL-predicted energy levels by 82 and of rovibrational transitions by 5382, and substantially reduces uncertainties of MARVEL-derived H₂CO energy levels over a large range: from pure rotational levels below 200 cm^-1 up to multiply excited vibrational levels at 6000 cm^-1. This work is an important step toward filling the gaps in formaldehyde data in the HITRAN database.