ExoMol line lists -- LII. Line Lists for the Methylidyne Cation (CH+)

Abstract

Comprehensive and accurate rovibronic line lists for the X ${}^1{\Sigma }^{+}$ and A ${}^1\Pi$ states of ${}^{12}$C${}^1$H${}^{+}$ and ${}^{13}$C${}^1$H${}^{+}$ which should be applicable up to temperatures of 5000 K are presented. Available empirical potential energy curves and high-level ab initio dipole and transition dipole moment curves are used with the program LEVEL to compute rovibronic energy levels and Einstein $A$ coefficients. $\Lambda$-doubling is incorporated into the energy levels and $A$-coefficients involving the A ${}^1\Pi$ state using an empirical method. For ${}^{12}$C${}^1$H${}^{+}$, line positions are improved by using both laboratory and astronomical observational spectra as input to the MARVEL procedure. The ${}^{12}$C${}^1$H${}^{+}$ line list contains 1505 states and 34194 transitions over the frequency range of 0 - 33010 cm${}^{-1}$ ($\lambda >300$ nm). Comparisons with observed astronomical and laboratory spectra give very good agreement. The PYT CH${}^{+}$ line lists and partition functions are available from the ExoMol database at www.exomol.com.