Insight into the Rydberg states of CH

Abstract

Ab initio electronic structure calculations of a relatively large number of Rydberg states of the CH radical were carried out employing the multireference single and double excitation configuration interaction (MRD-CI) method. A Gaussian basis set of cc-pV5Z quality augmented with 12 diffuse functions was used together with an extensive treatment of electron correlation. The main focus of this contribution is to investigate the 3d Rydberg complex assigned by Watson [Astrophys. J. 555, 472 (2001)] to three unidentified interstellar bands. The authors' calculations reproduce quite well the absolute excitation energies of the three components of the 3d complex, i.e., 2Sigma+(3dsigma), 2Pi(3dpi), and 2Delta(3ddelta), but not the energy ordering inferred from a rotational assignment of the 3d<--X 2Pi laboratory spectrum. The computation of the 4d complex is reported for the first time along with a number of other higher lying Rydberg species with an X 1Sigma+ core. The lowest Rydberg states belonging to series converging to the a 3Pi and A 1Pi excited states of CH+ are also calculated.

Photoionisation of the CH radical using the B-spline R-matrix method

“…These measurements have produced very precise descriptions of CH and CH + in their groundand excited electronic states. Several related theoretical studies have also been carried out on the lowest electronic states of CH and CH + (Baluja & Msezane 2001;Vázqueza et al 2007;Hamilton et al 2016;Chakrabarti et al 2017Chakrabarti et al , 2019.…”

CH in stellar atmospheres: an extensive linelist

“…This molecule was first detected by Heurlinger & Hulthen (1919) and then studied by many scientists (see references in Kalemos et al 1999). This molecule has many valence and Rydberg states as reviewed by Vázquez et al (2007), but only the lower energy states are of interest for stellar astrophysics. Our aim in this paper is to improve the situation for the ro-vibrational X 2 Π-X 2 Π and the A 2 Δ-X 2 Π, B 2 Σ − -X 2 Π, and C 2 Σ + -X 2 Π electronic transitions of CH (for both 12 CH and 13 CH isotopologues).…”

Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

“…The vibrational levels of the X 2 Π ground state have been studied up to the v=5 level; here we fix the rotational constants for the X 2 Π state to those presented in Masseron et al [4] who primarily used data from Colin and Bernath [9]. In addition to the experimental studies there are several high-level ab initio studies on the valence and Rydberg states [26][27][28]. Theoretical work on the potential energy curves of CH have predicted that the C 2 Σ + state interacts strongly with the yet unobserved 2 2 Σ + state [26,27].…”