Knowledge Bank

The \lq{}4050~\AA ~group\rq{} of C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$, which consists of a series of bands of the ~{A}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u$ - ~{X}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ electronic transition system, has been of much interest to astronomers as it serves as a remote diagnostic of the physical-chemical conditions in translucent interstellar clouds. In this contribution, we present: a) The high resolution ($R=80 000$) detection of eight vibronic bands of C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ in the diffuse translucent cloud towards HD~169454. Four of these vibronic bands are also detected in two additional objects: HD~73882 and HD~154368. Column densities and excitation conditions of C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ are inferred. b) A laboratory re-examination of the eight vibronic bands observed towards HD~169454 using cavity ring-down spectroscopy and a supersonic plasma jet. High-quality laboratory data build the list of lines with a wavelength accuracy of $\textless$0.01\backslash AA.Thisissufficientfortheanalysisoftheobservationaldata.Improvedspectroscopicparametersofthecorrespondingvibronicstatesarepresented.Animprovedperturbationanalysisinthe\backslash ~A$^{1}\Pi_{u}$ (000) state is given as well. c) The systematic laboratory investigation on the ~{A}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u$ - ~{X}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ 000-000 electronic origin band of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C-substituted C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$. Rotationally resolved spectra of all five $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C-isotopologues are recorded in a supersonic plasma expansion by discharging $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ or $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$/$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ mixtures diluted in noble gas. The ~{A}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi u$ state molecular constants for all five isotopologues and ground-state molecular constants for $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C and $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C are experimentally determined for the first time. This work extends the recent mid-infrared work on the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C-isotopologues of C$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ by Giesen \textit{et al.}