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arXiv · 2605.00564

High-resolution ro-vibrational and rotational spectroscopy of the open-shell, linear CCH$^+$ ion ($^3\Pi$)

Kim Steenbakkers·Weslley G. D. P. Silva·Oskar Asvany·Gerrit C. Groenenboom·Pavol Jusko·Britta Redlich·Sandra Brünken·Stephan Schlemmer
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Abstract

In this work, we report on the high-resolution infrared spectrum of CCH$^+$ ($^3\Pi$) recorded in the range $3066-3184$~cm$^{-1}$ by means of leak-out spectroscopy. This spectral range covers the fundamental of the CH stretching mode and a highly excited bending vibrational mode. Based on this data (385 ro-vibrational lines), accurate spectroscopic descriptions of the ground and the two vibrationally excited states of CCH$^+$ were obtained. Besides the band origins, spin-orbit coupling constants, rotational constants, centrifugal distortion constants and $\Lambda$-doubling constants for the ground and excited vibrational states have been derived. This effective Hamiltonian analysis allowed a search for pure rotational lines of CCH$^+$ in its electronic and vibrational ground state using a two-color millimeterwave - infrared scheme. We observed all rotational transitions from $J^{\prime\prime} = 2$ up to $J^{\prime\prime} = 6$ within the $\Omega = 2$ lowest energy fine structure component with resolved hyperfine splittings. This data has already guided the first detection of CCH$^+$ in space toward the Orion Bar photo-dissociation region, and has the potential to support further astronomical searches for CCH$^+$ either through radio or infrared spectroscopy, for example with the James Webb Space Telescope.

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Kim Steenbakkers, Weslley G. D. P. Silva, Oskar Asvany, Gerrit C. Groenenboom, Pavol Jusko, Britta Redlich, Sandra Brünken, Stephan Schlemmer. 2026-05-01. High-resolution ro-vibrational and rotational spectroscopy of the open-shell, linear CCH$^+$ ion ($^3\Pi$). https://doi.org/10.1021/acs.jpca.6c00521

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