HIGH RESOLUTION SPECTRUM OF THE $^{13}$C$^{12}$C$^{12}$C LOWEST BENDING MODE

Abstract

Linear C$_3$ is a floppy molecule which possesses an extremely low lying bending mode, $\nu_2$, at roughly 60 cm$^{-1}$ or 1.9 THz. Based on highly accurate laboratory data {\bf 249}, 897$-$900 (1990)}$^{,}$ {\bf 551}, L181$-$L184 (2001)}$^{,}$ {\bf 58a}, 129$-$138 (2003)} C$_3$ has been detected in various astronomical sources {\bf 73}, 67 (1995)}$^{,}$ {\bf 534}, L199$-$L202 (2000)} most recently with the HIFI instrument aboard the Herschel satellite {\bf 521}, L13 (2010)}. Although C$_3$ turns out to be quite abundant in interstellar environments which makes a search for $^{13}$C substituted isotopologs feasible, other isotopologs could not be detected so far, because no accurate transition frequencies have been available for these species in this frequency range. Relative abundance ratios of C$_3$ isotopologs might give important hints on its building mechanism and further constraints for chemical networks. In this work, the spectrum of the $\nu_2$ lowest bending mode of $^{13}$CCC has been investigated. We used laser ablation of $^{13}$C enriched carbon samples to record absorption spectra in a supersonic jet expansion. The radiation in our setup is generated by a synthesizer referenced to a Rubidium standard in combination with a frequency multiplier chain and detected by a liquid Helium cooled InSb bolometer. The laboratory search has been supported by high-level coupled-cluster calculations, which turns out to compare very favorably with obtained experimental molecular parameters.