Knowledge Bank

Gas-phase infrared spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$-substituted $C3$ molecules have been studied in the region of the $\nu 3$ vibration around $5\mu m$, using a tunable diode laser spectrometer and a hollow-cathode discharge in a flowing mixture of acetylene and helium. Three bands were observed and assigned: the $\nu 3$ fundamentals of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C3$ and of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C12C13C$, and the $\nu 3+\nu 2-\nu 2$ sequence band of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C3.$ The observed band origins are consistent with previous matrix-isolation spectroscopy of substituted $C3$. The rotational and centrifugal distortion parameters are consistent with previous gas-phase work on $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C3$, and they also reflect the highly anharmonic nature of the bending vibration in this molecule. The $\nu 3$ band of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C12C13C$, measured here for the first time, provides a sensitive means to measure $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ abundances in astrophysical sources containing $C3$.