INFRARED DIODE LASER SPECTROSCOPY OF $^{13}C_{3}$ AND $^{12}C^{12}C^{13}C$ IN THE $5 \mu m$ REGION

Abstract

Gas-phase infrared spectra of $^{13}C$-substituted $C_{3}$ 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 $^{13}C_{3}$ and of $^{12}C^{12}C^{13}C$, and the $\nu_{3}+\nu_{2}-\nu_{2}$ sequence band of $^{13}C_{3}.$ The observed band origins are consistent with previous matrix-isolation spectroscopy of substituted $C_{3}$. The rotational and centrifugal distortion parameters are consistent with previous gas-phase work on $^{12}C_{3}$, and they also reflect the highly anharmonic nature of the bending vibration in this molecule. The $\nu_{3}$ band of $^{12}C^{12}C^{13}C$, measured here for the first time, provides a sensitive means to measure $^{13}C$ abundances in astrophysical sources containing $C_{3}$.