Fourier-transform spectroscopy of the diatomic molecules in the VUV and UVis regions and precise analyse of the unimolecular interactions.

Diatomic molecules have enjoyed unflagging interest in various fields of science for many years. In the last two decades they have been at the centre of spectroscopic research due to new discoveries related to exoplanets [1,2]. Molecules such as CO, CO⁺, CH, CD, AlH and AlD play an important role in astrophysical space research [3,4]. Particular importance is attached to the detection and quantification of various natural isotopologues of these molecules in order to model the evolution of the universe, among others interstellar clouds and stars [5,6].

The vast majority of astronomical research is based solely on the results of precise atomic and molecular spectroscopy. In order to ensure high accuracy of the measurements, two precise and complementary high-resolution Fourier-transform (FT) spectroscopy technics were used to complete this purpose:

1. The vacuum ultraviolet (VUV) absorption spectra have been recorded using the FT spectrometer installed as a permanent end-station on the DESIRS beamline at the synchrotron SOLEIL facility in France [7];
2. ultraviolet (UV) and visible (VIS) emission spectra have been obtained using a 1.71-m Bruker spectrometer (IFS 125HR), located in the Materials Spectroscopy Laboratory (University of Rzeszów) [8].

The spectra were interpreted and the results were subjected to multi-level deperturbation analysis based on the effective Hamiltonian [9] and the method of simultaneous determination of molecular constants and terms [10]. This allowed for a complete description of the energy structure of electronic states by taking into account extensive and multi-state perturbations (Fig. 1), both homogeneous and heterogeneous, direct and indirect interactions [8,11,12].

Fig. 1. Ro-vibronic reduced terms (in cm^-1) of the A¹Π(v = 2) level and its perturbers in the ¹²C¹⁸O isotopologue [11].

References  

[1]           J. Tennyson and S. N. Yurchenko, ExoMol: Molecular Line Lists for Exoplanet and Other Atmospheres: ExoMol: Molecular Line Lists, Monthly Notices of the Royal Astronomical Society 425, 21 (2012).

[2]           J. Tennyson and S. Yurchenko, The ExoMol Atlas of Molecular Opacities, Atoms 6, 26 (2018).

[3]           G. Tinetti et al., A Chemical Survey of Exoplanets with ARIEL, Exp Astron 46, 135 (2018).

[4]           Y. Wang, J. Tennyson, and S. Yurchenko, Empirical Line Lists in the ExoMol Database, Atoms 8, 7 (2020).

[5]           J. Bally and W. D. Langer, Isotope-Selective Photodestruction of Carbon-Monoxide, Astrophysical Journal 255, 143 (1982).

[6]           C. J. Bennett, C. S. Jamieson, and R. I. Kaiser, Mechanistical Studies on the Formation and Destruction of Carbon Monoxide (CO), Carbon Dioxide (CO₂), and Carbon Trioxide (CO₃) in Interstellar Ice Analog Samples, Physical Chemistry Chemical Physics 12, 4032 (2010).

[7]           N. de Oliveira, D. Joyeux, M. Roudjane, J.-F. Gil, B. Pilette, L. Archer, K. Ito, and L. Nahon, The High-Resolution Absorption Spectroscopy Branch on the VUV Beamline DESIRS at SOLEIL, Journal of Synchrotron Radiation 23, 887 (2016).

[8]           R. Hakalla et al., Fourier-Transform Spectroscopy of ¹³C¹⁷O and Deperturbation Analysis of the A¹Π (v = 0–3) Levels, Journal of Quantitative Spectroscopy and Radiative Transfer 189, 312 (2017).

[9]           C. M. Western, PGOPHER: A Program for Simulating Rotational, Vibrational and Electronic Spectra, Journal of Quantitative Spectroscopy and Radiative Transfer 186, 221 (2017).

[10]        J. K. G. Watson, On the Use of Term Values in the Least-Squares Fitting of Spectra, J Mol Spectrosc 138, 302 (1989).

[11]        M. I. Malicka, S. Ryzner, A. N. Heays, N. de Oliveira, R. W. Field, W. Ubachs, and R. Hakalla, Deperturbation Analysis of the A¹Π (v = 2)  Level in the ¹²C¹⁸O Isotopologue, Journal of Quantitative Spectroscopy and Radiative Transfer 273, 107837 (2021).

[12]        S. Ryzner, M. I. Malicka, A. N. Heays, R. W. Field, N. de Oliveira, W. Szajna, W. Ubachs, and R. Hakalla, VUV–VIS FT Spectroscopy of the Rare ¹³C¹⁸O  Isotopologue of Carbon Monoxide: Analysis of the A¹Π (v = 1) Multiply-Perturbed Level, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 279, 121367 (2022).