The Synchrotron-based Far-infrared Spectrum of Propargylamine

Abstract Propargylamine (HC≡C–CH 2 –NH 2 ), with a triple bond and an amine group, is a nitrogen-bearing organic molecule of astrochemical interest due to its potential role as a precursor to aminoacetonitrile and other complex organic molecules in the interstellar medium (ISM). Despite the detection of the structurally related molecules propargylimine (HC≡C–CH=NH) and aminoacetonitrile (NH 2 –CH 2 –CN) in the ISM, it remains undetected. This work presents the first high-resolution far-infrared spectroscopic study of propargylamine, conducted using a synchrotron-based Fourier transform infrared spectrometer at the Canadian Light Source. The rotationally resolved vibrational spectra were measured in the range of 50–480 cm −1 , targeting its three lowest vibrational modes. The rovibrational analysis led to the assignment of two bands centered at 338.8342332(25) and 228.5012023(26) cm −1 , corresponding to the out-of-plane HC≡C–C linear bending ( ν 20 ) and –NH 2 torsion ( ν 21 ) modes, respectively. Also, a band origin of 199.10535(19) cm −1 was determined for the in-plane HC≡C–C linear bending ( ν 13 ) mode through a Coriolis-type resonance with the ν 21 mode. The accurate assignment clears up a discrepancy over these vibrational energy levels between previous millimeter-wave and low-resolution infrared studies and made possible the determination of an updated rovibrational partition function. These data provide spectroscopic parameters for future astronomical searches in the ISM.