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

TL;DR

This study employs optical frequency comb Fourier transform spectroscopy to obtain high-resolution spectra of formaldehyde, enhancing the MARVEL energy level analysis and contributing to more accurate molecular data for atmospheric and astrophysical applications.

Contribution

The paper provides a comprehensive high-resolution spectral line list for formaldehyde and improves the MARVEL analysis with new line positions, reducing uncertainties and expanding known energy levels.

Findings

747 rovibrational transitions identified and fitted

82 new energy levels added to MARVEL database

Significant reduction in energy level uncertainties

Abstract

We use optical frequency comb Fourier transform spectroscopy to record high-resolution, low-pressure, room-temperature spectra of formaldehyde (H$_2$$^{12}$C$^{16}$O) in the range of 1250 to 1390 cm$^{-1}$. Through line-by-line fitting, we retrieve line positions and intensities of 747 rovibrational transitions: 558 from the ${\nu}_6$ band, 129 from the ${\nu}_4$ band, and 14 from the ${\nu}_3$ 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 H$_2$CO 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 H$_2$CO 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.