The high-resolution infrared spectrum of the [formula omitted] combination band of jet-cooled propyne

K.D Doney,D Zhao,J Bouwman,H Linnartz

doi:10.1016/j.cplett.2017.07.022

Abstract

We present the first detection of the high-resolution ro-vibrational spectrum of the ν3+ν5 combination band of propyne around 3070cm−1. The fully resolved spectrum is recorded for supersonically jet-cooled propyne using continuous wave cavity ring-down spectroscopy (cw-CRDS). The assignments are supported with the help of accurate ab initio vibration-rotation interaction constants (αi) and anharmonic frequencies. A detailed analysis of the rotationally cold spectrum is given.

Highlights

Propyne, known as methylacetylene (H3CAC„CH), is a small unsaturated hydrocarbon of astrophysical importance
It is believed to play a role in the chemistry of a number of hydrocarbon-rich astronomical objects, including the atmosphere of Titan [1], the dark cloud TMC-1 [2], the circumstellar shell of the AGB star IRC+10216 [3], and two protoplanetary nebulae CRL 618 [4] and SMP LMC 11 [5], where it has been observed in the infrared (IR) through the m9 (HAC„C bending) mode, and by radio astronomy through pure rotational transitions
Studies of spectra that are perturbed through weak near-resonant couplings to background vibrational states, as seen in other transitions of propyne, make it of interest for studying intramolecular vibrational relaxation (IVR) [11,12,13,10,14,15,16,17]

Summary

Introduction

Known as methylacetylene (H3CAC„CH), is a small unsaturated hydrocarbon of astrophysical importance. It is believed to play a role in the chemistry of a number of hydrocarbon-rich astronomical objects, including the atmosphere of Titan [1], the dark cloud TMC-1 [2], the circumstellar shell of the AGB star IRC+10216 [3], and two protoplanetary nebulae CRL 618 [4] and SMP LMC 11 [5], where it has been observed in the infrared (IR) through the m9 (HAC„C bending) mode, and by radio astronomy through pure rotational transitions. The close spacing of the rotational transitions of different K0 subbands, and the relatively low dipole moment (l = 0.78 D) [6] make propyne an ideal probe of the interstellar medium’s kinetic temperature; since the excitation temperature increases as K0 increases [7,8,9]. Comparison between high-resolution measurements as presented here for propyne and ab initio methods offers a good test of the accuracy of the Hamiltonians used to describe the involved molecular energy levels

Methods

Results

Conclusion