Rotational spectra of isotopic species of methyl cyanide, CH$_3$CN, in their $v_8 = 1$ excited vibrational states

TL;DR

This study measures and analyzes the rotational spectra of isotopic methyl cyanide in excited vibrational states to support astronomical observations, providing precise spectroscopic data for minor isotopologs.

Contribution

It provides accurate spectroscopic parameters for isotopic methyl cyanide in their $v_8=1$ vibrational states, aiding astronomical detection and analysis.

Findings

Spectroscopic parameters obtained for three isotopic species.

Transitions identified up to 1.2 THz with good signal-to-noise.

Data supported identification of vibrational lines in space observations.

Abstract

Methyl cyanide is an important trace molecule in space, especially in star-forming regions where it is one of the more common molecules used to derive kinetic temperatures. We want to obtain accurate spectroscopic parameters of minor isotopologs of methyl cyanide in their lowest excited $v_8 = 1$ vibrational states to support astronomical observations, in particular, with interferometers such as ALMA. The laboratory rotational spectrum of methyl cyanide in natural isotopic composition has been recorded from the millimeter to the terahertz regions. Transitions with good signal-to-noise ratios could be identified for the three isotopic species CH$_3^{13}$CN, $^{13}$CH$_3$CN, and CH$_3$C(15)N up to about 1.2 THz ($J'' \le 66$). Accurate spectroscopic parameters were obtained for all three species. The present data were already instrumental in identifying $v_8 = 1$ lines of methyl cyanide with one $^{13}$C in IRAM 30 m and ALMA data toward Sagittarius B2(N).