| Abstract: | Calcium monohydride CaH is an astronomical molecule identified in the
Sun and other stars by using visible transitions.
We have found many new vibrational levels of the B/B$'$ state using
Laser Induced Fluorescence (LIF) from the visible to ultraviolet region.
$\footnote{K. Watanabe, N. Yoneyama, K. Uchida, K. Kobayashi, F.
Matsushima, Y. Moriwaki, S. C. Ross,
\textit{Chem. Phys. Lett.} \underline{\textbf{657}}, 1 (2016).}$$^,$
$\footnote{K. Watanabe, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross,
\textit{Chem. Phys. Lett.} \underline{\textbf{710}}, 11 (2018).}$
In the analysis of these transitions, we fixed the molecular constants
in the ground state to those analyzed for the A$^2\Pi$, B$^2\Sigma^+\rightarrow$ X$^2\Sigma^+$ in 12000 - 17000 cm$^{-1}$ region and the $v=v'+1\rightarrow v'$($v'=0-3$) in X$^2\Sigma^+$ transitions by Shayesteh
et al.
\footnote{A. Shayesteh, R. S. Ram, and P. F. Bernath, \textit{J. Mol.
Spectrosc.} \underline{\textbf{288}}, 46 (2013).}$^,$\footnote{A.
Shayesteh, K. A. Walker, I. Gordon, D. R. T. Appadoo, and P. F. Bernath,
\textit{J. Mol. Struct.}, \underline{695} (2004).}
The pure rotational spectra in the ground state have been reported and
hyperfine structure was analyzed.
$\footnote{ C. I. Frum, J. J. Oh, E. A. Cohen, H. M. Pickett, \textit{
Astrophys. J. Lett.} \underline{\textbf{408}}, L61 (1993).}$
$\footnote{ W. L. Barclay Jr., M. A. Anderson, L. M. Ziurys, \textit{
Astrophys. J. Lett.} \underline{\textbf{408}}, L65 (1993).}$
However, the range was limited up to $N$ = 2-1. the highest frequency
was about 500 GHz. In this study, we will report our new measurement in
the terahertz region.
The spectra were taken by using tunable far-infrared spectrometer at the
University of Toyama. Calcium monohydride was produced in a cell where
Ca vapor was introduced by heating Ca at 750$^\circ$C and DC discharge
was applied under H$_2$ and He gas environment. So far the highest
frequency we observed was about 1.5 THz. The accurate rest frequencies
and molecular constants will be provided. |
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