Rotational Spectroscopy as a Tool to Study Vibration-Rotation Interaction: Investigations of ¹³CH₃CN and CH₃¹³CN up to v₈ = 2 and a Search for v₈ = 2 Transitions toward Sagittarius B2(N)

2026/01/30 by Holger S. P. Müller, Arnaud Belloche, Frank Lewen +1 · 1 voice
Physics and Astronomy · #astro-ph.GA #astro-ph.IM #astro-ph.SR #physics.ao-ph #physics.chem-ph

paper · pdf · doi:10.1021/acsearthspacechem.5c00353

Abstract

Methyl cyanide, CH₃CN, is present in diverse regions in space, in particular in the warm parts of star-forming regions where it is a common molecule. Rotational transitions of ¹³CH₃CN and CH₃¹³CN in their v₈ = 1 lowest excited vibrational states (E_{\rm vib} ≈ 520 K) are quite prominent in Sagittarius B2(N). In order to be able to search for transitions of the next higher vibrational state v₈ = 2, we recorded spectra of samples enriched in ¹³CH₃CN and CH₃¹³CN up to v₈ = 2 in the 35 to 1091~GHz region and reinvestigated existing spectra of CH₃CN in its natural isotopic composition between 1085 and 1200 GHz. Perturbations caused by near-degeneracies in K = 4 of v₈ = 2⁰ and K = 2 of v₈ = 2^-2 yielded accurate information on the energy spacing of 22.93 and 21.79 cm^-1 between the l-components of ¹³CH₃CN and CH₃¹³CN, respectively. Fermi-type interaction between K = 13 and 14 of v₈ = 1^-1 and v₈ = 2⁺² probe the energy differences between the two states of both isotopomers. In addition, a ΔK ±2, Δl ∓1 interaction between the ground vibrational state of ¹³CH₃CN and v₈ = 1⁺¹ provides information on their energy spacing. Furthermore, we obtained improved or extended ground state rotational transition frequencies of ¹³CH₃¹³CN and extensive data for ¹³CH₃C¹⁵N and CH₃¹³C¹⁵N. Finally, we report the results of our search for transitions of ¹³CH₃CN and CH₃¹³CN in their v₈ = 2 states toward Sagittarius B2(N).

Citations

• Reexploring Molecular Complexity with ALMA: Insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2)
• First detection of 13CH in the interstellar medium
• Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2
• The ALMA-PILS survey: Complex nitriles towards IRAS 16293--2422
• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
• Exploring molecular complexity with ALMA (EMoCA): Alkanethiols and alkanols in Sagittarius B2(N2)
• Rotational spectra of isotopic species of methyl cyanide, CH₃CN, in their v₈ = 1 excited vibrational states
• Exploring Molecular Complexity with ALMA (EMoCA): Deuterated complex organic molecules in Sagittarius B2(N2)
• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• Rotational spectroscopy as a tool to investigate interactions between vibrational polyads in symmetric top molecules: low-lying states v₈ ≤ 2 of methyl cyanide, CH₃CN
• Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)
• The quest for complex molecules in space: Laboratory spectroscopy of n-butyl cyanide, n-C4H9CN, in the millimeter wave region and its astronomical search in Sagittarius B2(N)
• Weeds: a CLASS extension for the analysis of millimeter and sub-millimeter spectral surveys
• Rotational spectra of isotopic species of methyl cyanide, CH₃CN, in their ground vibrational states up to terahertz frequencies
• Rotational spectroscopy of isotopic vinyl cyanide, H₂C=CH-C≡N, in the laboratory and in space
• Density-functional thermochemistry. III. The role of exact exchange
• Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density

Discussions

• Rotational Spectroscopy as a Tool to Study Vibration-Rotation Interaction: Investigations of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN up to $v_8 = 2$ and a Search for $v_8 = 2$ Transitions toward Sagittari [bsky, 0 points, 0 comments]

Related

• Dataset related to the publication "Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370 cm-1 range of methane using optical frequency comb double-resonance spectroscopy"
• Rotational spectroscopy, tentative interstellar detection, and chemical modelling of N-methylformamide
• Revised gas-phase formation network of methyl cyanide: the origin of methyl cyanide and methanol abundance correlation in hot corinos
• Rotational Spectroscopy and Tentative Interstellar Detection of 3-Hydroxypropanal (HOCH₂CH₂CHO) in the G+0.693-0.027 Molecular Cloud
• Rotational Excitation of Vinyl Cyanide by Collisions with Helium Atoms at Low Temperature