Parallel Session: Fundamental, Contributed Talk (15min)

Spectroscopy of radioactive molecules 14CH4 and H36Cl

S. Larnimaa1, L. Halonen1, J. Karhu1, T. Tomberg1, M. Metsälä1, G. Genoud2, T. Hieta3, S. Bell4, V. Ulvila2, M. Vainio1,5*
1University of Helsinki, Department of Chemistry, Helsinki, Finland, 2VTT Technical Research Centre of Finland Limited, Espoo, Finland, 3Gasera Ltd., Turku, Finland, 4National Physical Laboratory, Middlesex, UK, 5Photonics Laboratory, Physics Unit, Tampere University, Tampere, Finland

Spectroscopy of radioactive compounds has gained extensive interest in recent years. Especially radiocarbon dioxide 14CO2 has been under thorough study with the motivation to develop optical instrumentation for its detection, for example, in nuclear facilities [1,2]. Another important radioactive molecule found in nuclear facilities is radiocarbon methane 14CH4 [3]. In a preliminary work [4], we reported the first absorption spectrum of 14CH4. More recently [5], we improved our results and reported high-resolution measurements and rotational analysis of the same fundamental asymmetric stretching vibrational band ν3(F2) of the molecule. We used a narrow linewidth, mid-infrared continuous-wave optical parametric oscillator combined with cantilever-enhanced photoacoustic spectroscopy and wavelength modulation spectroscopy to determine the line center wavenumbers of 43 rovibrational lines with 0.003 cm-1 uncertainty (95 % confidence level). In addition, a spectroscopic model was used in a non-linear least squares fit to confirm the experimental results and to determine the molecular constants. Our conference contribution presents this research on 14CH4 and on our yet unpublished Fourier-transform infrared spectroscopy measurements of the fundamental and first overtone rovibrational bands of H36Cl, a radioactive isotopologue of hydrogen chloride.

[1] Iacopo Galli, Saverio Bartalini, Riccardo Ballerini, Marco Barucci, Pablo Cancio, Marco De Pas, Giovanni Giusfredi, Davide Mazzotti, Naota Akikusa, Paolo De Natale, Optica, 2016, 3, 385-388.

[2] Guillaume Genoud, Johannes Lehmuskoski, Steven Bell, Vesa Palonen, Markku Oinonen, Mari-Leena Koskinen-Soivi, Matti Reinikainen, Analytical Chemistry, 2019, 91, 12315-12320.

[3] Man-Sung Yim, François Caron, Progress in Nuclear Energy, 2006, 48, 2-36.

[4] Juho Karhu, Teemu Tomberg, Francisco Senna Vieira, Guillaume Genoud, Vesa Hänninen, Markku Vainio, Markus Metsälä, Tuomas Hieta, Steven Bell, Lauri Halonen, Optics Letters, 2019, 44, 1142-1145.

[5] Santeri Larnimaa, Lauri Halonen, Juho Karhu, Teemu Tomberg, Markus Metsälä, Guillaume Genoud, Tuomas Hieta, Steven Bell, Markku Vainio, Chemical Physics Letters, 2020, 750, 137488.