The emission spectroscopy of the astrophysically significant B²Σ⁻–X²Π system of CD: further investigation

Abstract

The ${\mathrm{B}}^2{\mathrm{\Sigma }}^{-}-{\mathrm{X}}^2\mathrm{\Pi }$$(0-1)$ band has been identified and measured in the laboratory spectrum of the CD molecule for the first time. The emission from the discharge was observed with a high accuracy dispersive optical spectroscopy technique using a plane-grating spectrograph and recorded by a photomultiplier tube. In total, 99 ro-vibronic frequencies were measured with an absolute accuracy of about $\pm 0.010$ cm${}^{-1}$. In the following work, we present the results of the combined analysis of the current experimental data and the ${\mathrm{B}}^2{\mathrm{\Sigma }}^{-}-{\mathrm{X}}^2\mathrm{\Pi }$(0−0) [Szajna et al., J. Mol. Spectrosc. 324, 48–52 (2016)] and ${\mathrm{D}}^2{\mathrm{\Pi }}_i-{\mathrm{B}}^2{\mathrm{\Sigma }}^{-}$(0−0) [Herzberg and Johns, Astrophys. J. 158, 399–417 (1969)] bands of CD. The resulting data, compared to those from the earlier measurements, present more accurate molecular constants for the v = 0 vibrational level of the ${\mathrm{B}}^2{\mathrm{\Sigma }}^{-}$ and ${\mathrm{D}}^2{\mathrm{\Pi }}_i$ states. The parameters of the Λ-doubling (p, q) of the ${\mathrm{D}}^2{\mathrm{\Pi }}_i$(v = 0) level were obtained for the first time. The current observations and analysis have become a basis to discuss the possible detection of the CD radical in the interstellar medium by the $R_2(0.5)$, $Q_2(0.5)$+${}^Q{R}_{12}(0.5)$ and ${}^P{Q}_{12}(0.5)$ spectral lines of the ${\mathrm{B}}^2{\mathrm{\Sigma }}^{-}-{\mathrm{X}}^2\mathrm{\Pi }$$(0-0)$ band in the 3880 Å region.

GRAPHICAL ABSTRACT

Keywords:

• CD isotopologue
• ${\mathrm{B}}^2{\mathrm{\Sigma }}^{-}$ state
• ${\mathrm{D}}^2{\mathrm{\Pi }}_i$ state
• emission spectroscopy
• interstellar medium

Acknowledgements

We dedicate this work to Professor Wim Ubachs (Vrije Universiteit) on the occasion of his 65th birthday and in recognition of his outstanding contribution to laser and molecular spectroscopy as well as metrology leading into physics beyond the Standard Model.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Notes

1 Originally the lines were numbered by N value rather than by J value.

Additional information

Funding

We express our gratitude for the financial support of the European Regional Development Fund and the Polish state budget within the framework of the Carpathian Regional Operational Programme [grant number RPPK.01:03:00-18-001/10] for the period 2007–2013 through the funding of the Centre for Innovation and Transfer of Natural Science and Engineering Knowledge of the University of Rzeszów.