High-resolution Infrared Spectra Of The Ν1 Fundamental Bands Of 13c Mono-substituted Propyne In A Supersonic Slit Jet

In the past few decades, many high-resolution spectroscopic studies have been dedicated to the C-H stretch vibrations in propyne (CH$_3$-C$\equiv$CH), aiming to understand the intramolecular vibrational redistribution in isolated small hydrocarbons. In this talk, we present the sensitive detection of the $\nu_1$ (acetylenic C-H stretch) fundamental bands of the three $^{13}$C mono-substituted isotopologues of propyne. The infrared absorption spectra are recorded using continuous-wave cavity ring-down spectroscopy (CRDS) in combination with a supersonic jet expansion of propyne/argon gas mixtures. A 0.05x30 mm slit nozzle is used in the present experiment to realize an effective rotational cooling to $\approx$14 K and a reduced Doppler width of $\approx$90 MHz. The high sensitivity of CRDS allows us to detect the three $^{13}$C isotopologues in their 1.1\% natural abundance. Different infrared band intensities of $\nu_1$ are found for the three isotopologues. Detailed rotational analyses of the experimental spectra are performed to derive effective spectroscopic constants for the upper $\nu_1$ vibrational state. The $^{13}$C-substitution effect of the near/non-resonant perturbations to $\nu_1$ of propyne is discussed. In addition, more accurate infrared data of $^{12}$C-propyne, including the $\nu_1$ fundamental band, are also obtained from our experimental spectra