Fridolin Kwabia Tchana

Cyanogen (C₂N₂) has been suspected for a long time to be present in comets and to contribute to the creation of the CN radical. So far no observations with ground-based facilities have managed to detect this species, but the Rosetta mission, thanks to in situ observations with the ROSINA mass spectrometer, detected this species in the coma of 67P/Churyumov–Gerasimenko. To investigate its presence from infrared spectra in other comets, we developed a fluorescence model for the ν ₃ fundamental band. From new laboratory high-resolution infrared spectra of cyanogen, we analyzed the region of the ν ₃ band of C₂N₂, centered around 4.63 μm (2158 cm⁻¹). In addition to line positions and intensities, molecular parameters for the ground and excited vibrational state were obtained. These parameters allowed us to develop a fluorescence model for cyanogen. Line-by-line excitation rates of the ν ₃ band of cyanogen in cometary comae are presented. An upper limit of the abundance of cyanogen in a spectrum of comet C/2022 E3 (ZTF) is discussed.

The silane (SiH4) molecule is of importance for a wide range of fundamental and applied problems of physics, chemistry, astrophysics, and industry. We present here the newest and clearest complete quantitative analysis and modeling of line positions and intensities in the strongly absorbing ν2/ν4 bending dyad in the 830–1150 cm−1 spectral region. A database of calculated silane lines, SiCaSDa, is made available online through the Virtual Atomic and Molecular Data Centre (VAMDC).

The silane (SiH4) molecule is of importance for a wide range of fundamental and applied problems of physics, chemistry, astrophysics and industry. We present here the newest and clearest complete quantitative analysis and modeling of lines positions and intensities in the strongly absorbing nu2/nu4 bending dyad in the region near 900 cm-1. A database of calculated silane lines , SiCaSDa, is made available online through the Virtual Atomic and Molecular Data Centre (VAMDC) at (https://vamdc.icb.cnrs.fr/PHP/SiH4.php)

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200–350 K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200–350 K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42 m and by a THz radiation beam (82.5 GHz to 1.1 THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium.