13C MONO-SUBSTITUTED ISOTOPOLOGUES OF PROPYNE (H3CCCH): INVESTIGATING THE ACETYLENIC CH STRETCH PERTURBATION

The acetylenic CH stretch ($\nub{1}$) fundamental band of propyne is known to have a "double-crossing" type perturbation that shifts the $K’$-subbands out of normal order. To further investigate this perturbation, we present a combined experimental and \textit{ab initio} study on the jet-cooled high-resolution infrared spectra of the $\nub{1}$ fundamental band of the three mono-substituted $^{13}$C isotopologues of propyne: $^{13}$CH$_3$$^{12}$C$\equiv$$^{12}$CH, $^{12}$CH$_3$$^{13}$C$\equiv$$^{12}$CH, and $^{12}$CH$_3$$^{12}$C$\equiv$$^{13}$CH. The experimental spectra are recorded using continuous wave cavity ringdown spectroscopy (cw-CRDS), with the isotopologues produced at natural abundance in a continuous supersonic expansion of regular propyne diluted in argon and helium. The $K’$ = 0 and 1 subbands of all three isotopologues are measured near 3330~cm$^{-1}$.\footnote{K.D. Doney \textit{et al.}, J. Phys. Chem. A 122 (2), 582 (2018)