Abstract
SiH has long been observed in the spectrum of our Sun and other cool stars. Computed line lists for the main isotopologues of silicon monohydride, $^{28}$SiH, $^{29}$SiH, $^{30}$SiH and $^{28}$SiD are presented. These line lists consider rotation-vibration transitions within the ground $X$ $^{2}\Pi$ electronic state as well as transitions to the low-lying $A$ $^{2}\Delta$ and $a$ $^{4}\Sigma^-$ states. Ab initio potential energy (PECs) and dipole moment curves (DMCs) along with spin-orbit and electronic-angular-momentum couplings between them are calculated using the MRCI level of theory with the MOLPRO package. The PEC for the ground X $^2\Pi$ state is refined to available experimental data with a typical accuracy of around 0.01 cm$^{-1}$ or better. The $^{28}$SiH line list includes 11,785 rovibronic states and 1,724,841 transitions with associated Einstein-A coefficients for angular momentum $J$ up to $82.5$ and covering wavenumbers up to 31340 cm$^{-1}$ ($\lambda$ $<$ 0.319 $\mu$m). Spectra are simulated using the new line list and comparisons made with various experimental spectra. These line lists are applicable up to temperatures of ~5000 K, making them relevant to astrophysical objects such as exoplanetary atmospheres and cool stars and opening up the possibility of detection in the interstellar medium. These line lists are available at the ExoMol www.exomol.com and CDS database websites.
Highlights
Silicon hydride (SiH) is a free radical formed from the cosmically abundant elements of hydrogen and silicon, and is the simplest of the four possible silicon hydrides
Ab initio potential energy (PECs) and dipole moment curves (DMCs) along with spin-orbit and electronic-angular-momentum couplings between them are calculated using the multi-reference configuration interaction (MRCI) level of theory with the MOLPRO package
The ExoMol project aims at providing line lists of spectroscopic transitions for key molecular species which are likely to be important in the atmospheres of extrasolar planets and cool stars (Tennyson & Yurchenko 2012; Tennyson et al 2016c)
Summary
Silicon hydride (SiH) is a free radical formed from the cosmically abundant elements of hydrogen and silicon, and is the simplest of the four possible silicon hydrides. The first recorded wavelengths for SiH were for the A 2∆ – X 2Π system starting with Jackson (1930), with the most recent study by Ram et al (1998) building on earlier work (Rochester 1936; Douglas 1957; Verma 1965; Singh & Vanlandingham 1978; Klynning et al 1979) Spectra for this system were recorded in the gas phase as part of silane glow discharge studies (Nemoto et al 1989; Washida et al 1985; Perrin & Delafosse 1980; Stamou et al 1997). The ExoMol project aims at providing line lists of spectroscopic transitions for key molecular species which are likely to be important in the atmospheres of extrasolar planets and cool stars (Tennyson & Yurchenko 2012; Tennyson et al 2016c).
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