Spectroscopic parameters and rest frequencies of isotopic methylidynium, CH+

TL;DR

This paper provides precise spectroscopic parameters and rest frequencies for various isotopologs of methylidynium (CH+), aiding astronomical spectral analysis with Herschel and SOFIA by resolving previous frequency discrepancies.

Contribution

The study derives accurate spectroscopic parameters and rest frequencies for six CH+ isotopologs using laboratory spectra and least-squares fitting, supporting astronomical observations.

Findings

Accurate rest frequencies for six CH+ isotopologs were determined.

Laboratory data improved the spectral database for astronomical applications.

The results resolve previous frequency discrepancies in astronomical observations.

Abstract

Astronomical observations toward Sagittarius B2(M) as well as other sources with APEX have recently suggested that the rest frequency of the J = 1 - 0 transitions of 13CH+ is too low by about 80 MHz. Improved rest frequencies of isotopologs of methylidynium should be derived to support analyses of spectral recording obtained with the ongoing Herschel mission or the upcoming SOFIA. Laboratory electronic spectra of four isotopologs of CH+ have been subjected to one global least-squares fit. Laboratory data for the J = 1 - 0 ground state rotational transitions of CH+, 13CH+, and CD+, which became available during the refereeing process, have been included in the fit as well. An accurate set of spectroscopic parameters has been obtained together with equilibrium bond lengths and accurate rest frequencies for six CH+ isotopologs: CH+, 13CH+, 13CD+, CD+, 14CH+, and CT+. The present data will be useful for the analyses of $Herschel$ or SOFIA observations of methylidynium isotopic species.